feat(metadata): add OpenModelDB metadata provider and model source for upscalers

Add OpenModelDB (openmodeldb.info) as a metadata and download source for
the existing upscaler model type.

Metadata:
- New OpenModelDBClient: fetches the site's bulk JSON dumps, caches them
  on disk (24h TTL + ETag revalidation), and builds a local sha256 index
- New OpenModelDBModelMetadataProvider adapts catalogue entries to the
  CivitAI-shaped version dict contract; registered in the fallback chain
  behind the enable_openmodeldb_api setting (default on), gated to the
  upscaler sub-type so other model types never trigger the dump download
- Persisted provenance uses metadata_source "openmodeldb" plus a nested
  openmodeldb block (page URL, architecture, scale, license)

Images: paired-image LR/SR URLs are ephemeral imgdiff.net sessions, so
displayable images come from the site-hosted auto-generated thumbnails
(model-level cover leads images[], per-image thumbs for the rest); the
original comparison URL is kept in meta.comparisonUrl.

Downloads:
- New OpenModelDBSource (flat model ids, omdb: group prefix) with
  resource filename derivation that recovers names hidden mid-path
  (mediafire) or synthesizes {id}.{type} for folder links
- HTML-gateway mirrors (mediafire/mega/drive) are rejected with a clear
  manual-download hint instead of silently saving an HTML page as .pth
- ModelSource base gains is_valid_source_id / default_subdir_parts /
  resolve_download_url hooks so flat-id sources need no platform branches

UI: "View on OpenModelDB" link in the model modal (downloaded and
hash-enriched models), settings toggle next to the CivArchive one.

locales/de.json

@@ -793,6 +793,8 @@
             "downloadComplete": "Download erfolgreich abgeschlossen",
             "enableCivarchiveApi": "CivArchive API als Metadaten-Anbieter aktivieren",
             "enableCivarchiveApiHelp": "Wenn aktiviert, wird die CivArchive API als alternative Quelle für Modell-Metadaten verwendet (z. B. für von CivitAI gelöschte Modelle). Deaktivieren, um die Ratenbegrenzungen von CivArchive vollständig zu vermeiden.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "Reihenfolge der Metadaten-Anbieter",
             "providerOrderHelp": "Die CivitAI API wird immer zuerst versucht. Wählen Sie die Reihenfolge der übrigen Anbieter bei der Metadatensuche.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/en.json

@@ -793,6 +793,8 @@
       "downloadComplete": "Download completed successfully",
       "enableCivarchiveApi": "Enable CivArchive API as metadata provider",
       "enableCivarchiveApiHelp": "When on, CivArchive API is used as a fallback source for model metadata (e.g. for models deleted from CivitAI). Turn off to avoid CivArchive rate limits entirely.",
+      "enableOpenmodeldbApi": "Enable OpenModelDB as metadata provider",
+      "enableOpenmodeldbApiHelp": "When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
       "providerOrder": "Metadata provider fallback order",
       "providerOrderHelp": "CivitAI API is always tried first. Choose the order of the remaining providers when looking up metadata.",
       "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/es.json

@@ -793,6 +793,8 @@
             "downloadComplete": "Descarga completada exitosamente",
             "enableCivarchiveApi": "Habilitar CivArchive API como proveedor de metadatos",
             "enableCivarchiveApiHelp": "Al activarlo, la API de CivArchive se usa como fuente alternativa de metadatos de modelos (p. ej. para modelos eliminados de CivitAI). Desactívelo para evitar por completo los límites de velocidad de CivArchive.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "Orden de proveedores de metadatos de respaldo",
             "providerOrderHelp": "La API de CivitAI siempre se intenta primero. Elija el orden de los demás proveedores al buscar metadatos.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/fr.json

@@ -793,6 +793,8 @@
             "downloadComplete": "Téléchargement terminé avec succès",
             "enableCivarchiveApi": "Activer l'API CivArchive comme fournisseur de métadonnées",
             "enableCivarchiveApiHelp": "Lorsqu'elle est activée, l'API CivArchive est utilisée comme source de secours pour les métadonnées des modèles (par ex. pour les modèles supprimés de CivitAI). Désactivez pour éviter entièrement les limites de débit de CivArchive.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "Ordre de secours des fournisseurs de métadonnées",
             "providerOrderHelp": "L'API CivitAI est toujours essayée en premier. Choisissez l'ordre des autres fournisseurs lors de la recherche de métadonnées.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/he.json

@@ -793,6 +793,8 @@
             "downloadComplete": "ההורדה הושלמה בהצלחה",
             "enableCivarchiveApi": "הפעל את CivArchive API כספק מטא-נתונים",
             "enableCivarchiveApiHelp": "כאשר מופעל, CivArchive API משמש כמקור גיבוי למטא-נתונים של מודלים (למשל עבור מודלים שנמחקו מ-CivitAI). כבה כדי להימנע לחלוטין ממגבלות הקצב של CivArchive.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "סדר ספקי מטא-נתונים לגיבוי",
             "providerOrderHelp": "CivitAI API תמיד מנוסה ראשון. בחר את סדר הספקים הנותרים בעת חיפוש מטא-נתונים.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/ja.json

@@ -793,6 +793,8 @@
             "downloadComplete": "ダウンロードが正常に完了しました",
             "enableCivarchiveApi": "CivArchive API をメタデータプロバイダーとして有効化",
             "enableCivarchiveApiHelp": "有効にすると、CivArchive API がモデルメタデータの代替ソースとして使用されます（例：CivitAI から削除されたモデルの場合）。オフにすると、CivArchive のレート制限を完全に回避できます。",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "メタデータプロバイダーのフォールバック順序",
             "providerOrderHelp": "CivitAI API が常に最初に試行されます。メタデータ検索時の残りのプロバイダーの順序を選択してください。",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/ko.json

@@ -793,6 +793,8 @@
             "downloadComplete": "다운로드가 성공적으로 완료되었습니다",
             "enableCivarchiveApi": "CivArchive API를 메타데이터 제공자로 활성화",
             "enableCivarchiveApiHelp": "활성화하면 CivArchive API가 모델 메타데이터의 대체 소스로 사용됩니다 (예: CivitAI에서 삭제된 모델의 경우). 비활성화하면 CivArchive의 속도 제한을 완전히 피할 수 있습니다.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "메타데이터 제공자 폴백 순서",
             "providerOrderHelp": "CivitAI API가 항상 먼저 시도됩니다. 메타데이터 조회 시 나머지 제공자의 순서를 선택하세요.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/ru.json

@@ -793,6 +793,8 @@
             "downloadComplete": "Загрузка успешно завершена",
             "enableCivarchiveApi": "Включить CivArchive API как источник метаданных",
             "enableCivarchiveApiHelp": "При включении CivArchive API используется как резервный источник метаданных моделей (например, для моделей, удалённых с CivitAI). Отключите, чтобы полностью избежать ограничений скорости CivArchive.",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "Порядок резервных источников метаданных",
             "providerOrderHelp": "CivitAI API всегда проверяется первым. Выберите порядок остальных источников при поиске метаданных.",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/zh-CN.json

@@ -793,6 +793,8 @@
             "downloadComplete": "下载成功完成",
             "enableCivarchiveApi": "启用 CivArchive API 作为元数据提供者",
             "enableCivarchiveApiHelp": "开启后，CivArchive API 将作为模型元数据的备用来源（例如用于已从 CivitAI 删除的模型）。关闭可完全避免 CivArchive 的速率限制。",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "元数据提供者回退顺序",
             "providerOrderHelp": "CivitAI API 始终优先尝试。选择查找元数据时其余提供者的顺序。",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",

locales/zh-TW.json

@@ -793,6 +793,8 @@
             "downloadComplete": "下載成功完成",
             "enableCivarchiveApi": "啟用 CivArchive API 作為中繼資料提供者",
             "enableCivarchiveApiHelp": "開啟後，CivArchive API 將作為模型中繼資料的備用來源（例如用於已從 CivitAI 刪除的模型）。關閉可完全避免 CivArchive 的速率限制。",
+            "enableOpenmodeldbApi": "[TODO: Translate] Enable OpenModelDB as metadata provider",
+            "enableOpenmodeldbApiHelp": "[TODO: Translate] When on, upscaler metadata is also looked up in the OpenModelDB catalogue (openmodeldb.info) when CivitAI has no record. The catalogue is cached locally and refreshed daily.",
             "providerOrder": "中繼資料提供者回退順序",
             "providerOrderHelp": "CivitAI API 始終優先嘗試。選擇查詢中繼資料時其餘提供者的順序。",
             "providerOrderCivitaiArchiveSqlite": "CivitAI → CivArchive → Archive DB",