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/ModelCard.js

@@ -1,4 +1,5 @@
 import { showToast, openCivitai, openHuggingFace, copyToClipboard, copyLoraSyntax, sendLoraToWorkflow, sendEmbeddingToWorkflow, openExampleImagesFolder, buildLoraSyntax, sendModelPathToWorkflow } from '../../utils/uiHelpers.js';
+import { getModelSourceInfo, getModelSourceGroupKey, getModelSourceViewTitle, openModelSource } from '../../utils/modelSourceHelpers.js';
 import { state, getCurrentPageState } from '../../state/index.js';
 import { showModelModal } from './ModelModal.js';
 import { hasCivitaiSource } from './utils.js';
@@ -65,12 +66,15 @@ function handleModelCardEvent_internal(event, modelType) {
     if (event.target.closest('.fa-globe')) {
         event.stopPropagation();
         // CivitAI wins when the model actually has CivitAI data; otherwise fall
-        // back to HuggingFace. Relying on `from_civitai` here made the two
-        // sources mutually exclusive whenever one of them was (re)linked (#1094).
+        // back to the linked external source. Relying on `from_civitai` here
+        // made the two sources mutually exclusive whenever one of them was
+        // (re)linked (#1094).
         if (card.dataset.has_civitai === 'true') {
             openCivitai(card.dataset.filepath);
-        } else if (card.dataset.hf_url) {
+        } else if (card.dataset.source_platform === 'huggingface' && card.dataset.hf_url) {
             openHuggingFace(card.dataset.hf_url);
+        } else if (card.dataset.source_url) {
+            openModelSource(card.dataset.source_url);
         }
         return true; // Stop propagation
     }
@@ -337,6 +341,8 @@ async function showModelModalFromCard(card, modelType) {
         modified: card.dataset.modified,
         file_size: parseInt(card.dataset.file_size || '0'),
         from_civitai: card.dataset.from_civitai === 'true',
+        source_platform: card.dataset.source_platform || '',
+        source_url: card.dataset.source_url || '',
         hf_url: card.dataset.hf_url || '',
         base_model: card.dataset.base_model,
         notes: card.dataset.notes || '',
@@ -428,6 +434,8 @@ function showExampleAccessModal(card, modelType) {
                 modified: card.dataset.modified,
                 file_size: card.dataset.file_size,
                 from_civitai: card.dataset.from_civitai === 'true',
+                source_platform: card.dataset.source_platform || '',
+                source_url: card.dataset.source_url || '',
                 hf_url: card.dataset.hf_url || '',
                 base_model: card.dataset.base_model,
                 notes: card.dataset.notes,
@@ -490,7 +498,11 @@ export function createModelCard(model, modelType) {
     card.dataset.base_model = model.base_model || 'Unknown';
     card.dataset.favorite = model.favorite ? 'true' : 'false';
     card.dataset.exclude = model.exclude ? 'true' : 'false';
-    card.dataset.hf_url = model.hf_url || '';
+    const modelSourceInfo = getModelSourceInfo(model);
+    card.dataset.source_url = modelSourceInfo?.url || '';
+    card.dataset.source_platform = modelSourceInfo?.platform || '';
+    // Legacy alias: only Hugging Face models expose `hf_url`.
+    card.dataset.hf_url = modelSourceInfo?.platform === 'huggingface' ? modelSourceInfo.url : '';
     const hasUpdateAvailable = Boolean(model.update_available);
     card.dataset.update_available = hasUpdateAvailable ? 'true' : 'false';
     card.dataset.skip_metadata_refresh = model.skip_metadata_refresh ? 'true' : 'false';
@@ -508,11 +520,12 @@ export function createModelCard(model, modelType) {
     const modelId = civitaiData?.modelId ?? civitaiData?.model_id;
     if (modelId !== undefined && modelId !== null && modelId !== '') {
         card.dataset.modelId = modelId;
-    } else if (model.hf_url) {
-        // For HF-only models, derive a group key from hf_url for version grouping
-        const match = model.hf_url.match(/https?:\/\/huggingface\.co\/([^/]+\/[^/]+)/);
-        if (match) {
-            card.dataset.modelId = 'hf:' + match[1];
+    } else {
+        // For externally-sourced models, derive a group key from the source
+        // URL for version grouping (hf:user/repo, ms:user/repo, ta:<id>).
+        const sourceGroupKey = getModelSourceGroupKey(model);
+        if (sourceGroupKey) {
+            card.dataset.modelId = sourceGroupKey;
         }
     }
 
@@ -610,10 +623,10 @@ export function createModelCard(model, modelType) {
     const hasCivitai = hasCivitaiSource(model.civitai);
     const globeTitle = hasCivitai ?
         translate('modelCard.actions.viewOnCivitai', {}, 'View on Civitai') :
-        model.hf_url ?
-            translate('modelCard.actions.viewOnHuggingFace', {}, 'View on Hugging Face') :
+        modelSourceInfo ?
+            getModelSourceViewTitle(modelSourceInfo) :
             translate('modelCard.actions.notAvailableFromCivitai', {}, 'Not available from Civitai');
-    const globeEnabled = hasCivitai || !!model.hf_url;
+    const globeEnabled = hasCivitai || !!modelSourceInfo;
     let sendTitle;
     let copyTitle;
     if (modelType === MODEL_TYPES.LORA) {