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.

templates/components/context_menu.html

@@ -21,7 +21,7 @@
                 <i class="fas fa-external-link-alt"></i> <span>{{ t('loras.contextMenu.linkCivitai') }}</span>
             </div>
             <div class="context-menu-item" data-action="link-hf">
-                <i class="fas fa-robot"></i> <span>{{ t('loras.contextMenu.linkHuggingFace') }}</span>
+                <i class="fas fa-robot"></i> <span>{{ t('loras.contextMenu.linkModelSource') }}</span>
             </div>
         </div>
     </div>

templates/components/modals/link_hf_modal.html

@@ -1,24 +1,29 @@
-<!-- Link to HuggingFace Modal -->
+<!-- Link to Model Source Modal -->
 <div id="linkHfModal" class="modal">
     <div class="modal-content">
         <button class="close" onclick="modalManager.closeModal('linkHfModal')">&times;</button>
-        <h2>{{ t('modals.linkHuggingFace.title') }}</h2>
+        <h2>{{ t('modals.linkModelSource.title') }}</h2>
         <div class="warning-box">
             <i class="fas fa-info-circle"></i>
-            <p>{{ t('modals.linkHuggingFace.infoText') }}</p>
+            <p>{{ t('modals.linkModelSource.infoText') }}</p>
         </div>
         <div class="input-group">
-            <label for="hfModelUrl">{{ t('modals.linkHuggingFace.urlLabel') }}</label>
-            <input type="text" id="hfModelUrl" placeholder="{{ t('modals.linkHuggingFace.urlPlaceholder') }}" />
+            <label for="hfModelUrl">{{ t('modals.linkModelSource.urlLabel') }}</label>
+            <input type="text" id="hfModelUrl" placeholder="{{ t('modals.linkModelSource.urlPlaceholder') }}" />
             <div class="input-error" id="hfModelUrlError"></div>
             <div class="input-help">
-                {{ t('modals.linkHuggingFace.helpText') }}<br>
-                <strong>https://huggingface.co/user/repo</strong>
+                {{ t('modals.linkModelSource.helpText') }}
+                <div id="hfSupportedSources">
+                    <strong>https://huggingface.co/user/repo</strong><br>
+                    <strong>https://modelscope.cn/models/user/repo</strong><br>
+                    <strong>https://tensor.art/models/827823520299086029</strong>
+                </div>
+                {{ t('modals.linkModelSource.enrichNote') }}
             </div>
         </div>
         <div class="modal-actions">
             <button class="cancel-btn" onclick="modalManager.closeModal('linkHfModal')">{{ t('common.actions.cancel') }}</button>
-            <button class="confirm-btn" id="confirmLinkHfBtn">{{ t('modals.linkHuggingFace.confirmAction') }}</button>
+            <button class="confirm-btn" id="confirmLinkHfBtn">{{ t('modals.linkModelSource.confirmAction') }}</button>
         </div>
     </div>
 </div>