feat(links): support ModelScope and TensorArt as model sources

A model file could only ever be linked to huggingface.co: `set_hf_url`
validated the URL with a huggingface-only regex, the agent fetched the card
from a hardcoded HF URL, and the readme processor built every relative image
path off `https://huggingface.co/{repo}/resolve/main`. ModelScope publishes the
same model-card convention (README.md + YAML frontmatter, often carrying
`base_model:` and `trigger_words:`) behind a public, key-less API, so the
enrichment pipeline could already serve it - it was the plumbing that was
HF-shaped, not the idea.

Make the external source a first-class, provider-driven concept:

- New `py/services/model_sources/` registry. A `ModelSource` owns URL
  recognition (lenient for stored values, strict for user input), the
  canonical page URL, model-card fetching, the asset base URL and the
  capability flags. `HuggingFaceSource` is the previous logic relocated;
  `ModelScopeSource` reads `/models/{o}/{n}/resolve/{master|main}/README.md`
  and falls back to `/api/v1/models/{o}/{n}/repo`. `TensorArtSource` is
  link-only on purpose: tensor.art answers plain HTTP clients with a
  Cloudflare challenge and its internal API (ap-east-1.tensorart.cloud /
  cn.tensorart.net) rejects every /v1/model/* route with "invalid
  authorization header", so it declares supports_enrichment=False rather than
  failing silently later.
- Metadata gains `source_platform` + `source_url`; `hf_url` stays as a
  read/write alias, written only for Hugging Face, so existing sidecars,
  cached rows and third-party consumers keep working. Normalisation runs at
  the scanner, the persistent cache (both directions, plus two new columns
  behind an ALTER migration) and the linking handler - which is what stops a
  user who switches sources from leaving a stale `hf_url` on a ModelScope
  model.
- The agent pipeline keys off the provider instead of `hf_url`: the fast-fail
  gate now explains *why* a model is skipped (no source / unknown source /
  source without a reachable card), the prompt context exposes
  source_url/source_id/source_label/asset_base_url while still filling the
  legacy hf_url/repo aliases, and the four README image extractors take a
  base_url (defaulting to HF) so relative paths resolve against the right
  site. Version grouping generalises to hf: / ms: / ta: keys.
- `POST /api/lm/set-hf-url` keeps its path and its legacy payload keys but
  accepts `source_url`, validates against every provider and returns the
  platform. `GET /api/lm/model-sources` lets the UI render the supported-site
  list from the server.
- Frontend: a `modelSourceHelpers` mirror of the registry drives the link
  dialog, the card/modal globe (branded "View on ModelScope/TensorArt"), the
  version-group key and the enrichment gate; the versions tab no longer sends
  ms:/ta: keys to the CivitAI API.

TensorArt stays in the list because provenance is worth keeping even when the
card is unreadable - the dialog says so plainly ("Sites that don't expose one
(currently TensorArt) can only be linked") and the context menu disables
enrichment with a matching tooltip, instead of the user getting
"Unsupported URL".

Verified against the real ModelScope API: jj3550945163/Krea-2-LORA returns a
1882-byte card whose frontmatter carries base_model/tags/trigger_words, and
relative images resolve to .../resolve/master/....

Tests: backend 2815 passed; frontend 1130 JS + 91 Vue passed; pytest
tests/i18n and a Jinja compile pass over templates/. The nine locales carry
[TODO: Translate] for the new strings, completed in the next commit.

static/js/components/shared/ModelModal.js

@@ -1,4 +1,5 @@
 import { showToast, openCivitai, sendLoraToWorkflow, sendEmbeddingToWorkflow, sendModelPathToWorkflow, buildLoraSyntax, copyToClipboard } from '../../utils/uiHelpers.js';
+import { getModelSourceInfo, getModelSourceGroupKey, getModelSourceViewTitle, openModelSource } from '../../utils/modelSourceHelpers.js';
 import { modalManager } from '../../managers/ModalManager.js';
 import { MODEL_TYPES } from '../../api/apiConfig.js';
 import {
@@ -397,10 +398,13 @@ export async function showModelModal(model, modelType) {
 <div class="civitai-view" title="${translate('modals.model.actions.viewOnCivitai', {}, 'View on Civitai')}" data-action="view-civitai" data-filepath="${escapedFilePathAttr}">
     <i class="fas fa-globe"></i> ${translate('modals.model.actions.viewOnCivitaiText', {}, 'View on Civitai')}
 </div>`.trim() : '';
-    const escapedHfUrl = modelWithFullData.hf_url ? escapeAttribute(modelWithFullData.hf_url) : '';
-    const viewOnHuggingFaceAction = escapedHfUrl ? `
-<div class="civitai-view" title="${translate('modals.model.actions.viewOnHuggingFace', {}, 'View on Hugging Face')}" data-action="view-huggingface" data-hf-url="${escapedHfUrl}">
-    <i class="fas fa-globe"></i> ${translate('modals.model.actions.viewOnHuggingFaceText', {}, 'View on Hugging Face')}
+    const sourceInfo = getModelSourceInfo(modelWithFullData);
+    const escapedSourceUrl = sourceInfo?.url ? escapeAttribute(sourceInfo.url) : '';
+    const isHuggingFaceSource = sourceInfo?.platform === 'huggingface';
+    const sourceTitle = sourceInfo ? getModelSourceViewTitle(sourceInfo) : '';
+    const viewOnHuggingFaceAction = escapedSourceUrl ? `
+<div class="civitai-view" title="${escapeAttribute(sourceTitle)}" data-action="${isHuggingFaceSource ? 'view-huggingface' : 'view-model-source'}" ${isHuggingFaceSource ? 'data-hf-url' : 'data-source-url'}="${escapedSourceUrl}">
+    <i class="fas fa-globe"></i> ${escapeHtml(sourceTitle)}
 </div>`.trim() : '';
     const creatorInfoAction = modelWithFullData.civitai?.creator ? `
 <div class="creator-info" data-username="${modelWithFullData.civitai.creator.username}" data-action="view-creator" title="${translate('modals.model.actions.viewCreatorProfile', {}, 'View Creator Profile')}">
@@ -520,12 +524,12 @@ export async function showModelModal(model, modelType) {
     const loadingExamplesText = translate('modals.model.loading.examples', {}, 'Loading examples...');
 
     const loadingVersionsText = translate('modals.model.loading.versions', {}, 'Loading versions...');
-    // Use CivitAI modelId, or derive HF group key for HF-only models
+    // Use CivitAI modelId, or derive a source group key for externally-linked models
     let civitaiModelId = modelWithFullData.civitai?.modelId || '';
-    if (!civitaiModelId && modelWithFullData.hf_url) {
-        const match = modelWithFullData.hf_url.match(/https?:\/\/huggingface\.co\/([^/]+\/[^/]+)/);
-        if (match) {
-            civitaiModelId = 'hf:' + match[1];
+    if (!civitaiModelId) {
+        const sourceGroupKey = getModelSourceGroupKey(modelWithFullData);
+        if (sourceGroupKey) {
+            civitaiModelId = sourceGroupKey;
         }
     }
     const civitaiVersionId = modelWithFullData.civitai?.id || '';
@@ -939,6 +943,11 @@ function setupEventHandlers(filePath, modelType) {
                     window.open(target.dataset.hfUrl, '_blank', 'noopener,noreferrer');
                 }
                 break;
+            case 'view-model-source':
+                if (target.dataset.sourceUrl) {
+                    openModelSource(target.dataset.sourceUrl);
+                }
+                break;
             case 'view-creator':
                 const username = target.dataset.username;
                 if (username) {