i18n: translate the download progress stage strings

Fill in the 4 `modals.download.progress.*` keys added by the previous
commit across all 9 locales, so no `[TODO: Translate]` placeholder remains
and the "no remaining placeholders" claim in the guidelines holds again.

No new terminology: `metadata` reuses the §5 row (fr métadonnées, de
Metadaten, es metadatos, ru метаданные, he מטא-נתונים, ja メタデータ,
ko 메타데이터, zh-CN 元数据, zh-TW 中繼資料) and the fetching phrasing
mirrors each locale's existing `download.fetchingRepoFiles` /
`fetchingVersions` (de passive "werden abgerufen", es "Obteniendo", fr
"Récupération des", ru "Получение", he "מביא", ja "取得中", ko "가져오는
중"). "model file" follows `errors.noModelFiles` in each file.

`{name}` and `{source}` are verbatim §1-R2 placeholders. `{source}` is
replaced at runtime with the *untranslated* platform name, so its
surrounding spacing follows each locale's `modelCard.actions.viewOnSource`
precedent — ja `{source} から`, ko `{source}에서`, zh `从 {source}` /
`從 {source}`, he `מ-{source}` (as in the existing `מ-CivitAI`), ru
`из {source}` (as in `из Workflow`) — and no brand ever appears inside the
translated text.

Punctuation: ASCII `:` for the Latin / Cyrillic / Hebrew locales and for
ja / ko, whose four sibling keys in the same `progress` block already use
ASCII; French keeps this file's ` : `; zh-CN / zh-TW use full-width `：`
like their siblings.

The guidelines gain a status block recording the pass and those spacing
precedents, so a future source added to the same slot does not have to
re-derive them.

Verified: `pytest tests/i18n/test_i18n.py` 20 passed,
`sync_translation_keys.py --dry-run` reports no drift, `npm test` exits 0
(1259 JS + 91 Vue). Each locale file gains exactly 4 lines — the values
were substituted as literals rather than re-serialising the JSON, so no
formatting churn.

locales/zh-TW.json

@@ -1488,10 +1488,10 @@
             "progress": {
                 "currentFile": "目前檔案：",
                 "downloading": "下載中：{name}",
-                "metadata": "[TODO: Translate] Metadata: {name}",
-                "indexingFile": "[TODO: Translate] Reading model file...",
-                "fetchingSourceMetadata": "[TODO: Translate] Fetching metadata from {source}...",
-                "fetchingMetadata": "[TODO: Translate] Fetching metadata...",
+                "metadata": "中繼資料：{name}",
+                "indexingFile": "正在讀取模型檔案...",
+                "fetchingSourceMetadata": "正在從 {source} 取得中繼資料...",
+                "fetchingMetadata": "正在取得中繼資料...",
                 "transferred": "已下載：{downloaded} / {total}",
                 "transferredSimple": "已下載：{downloaded}",
                 "transferredUnknown": "已下載：--",