feat(hf): add Link to HuggingFace feature with unified Link Model submenu

- Merge Relink to Civitai and new Link to HuggingFace into a single
  'Link Model' submenu with sub-options for each source
- Add POST /api/lm/set-hf-url endpoint to associate a model with a
  HuggingFace repo URL, saving hf_url to .metadata.json
- Add link_hf_modal.html for URL input, following relink-civitai pattern
- Use update_single_model_cache instead of add_model_to_cache to
  prevent duplicate cache entries after linking
- Remove os.path.realpath usage for consistency with relink-civitai
- Raise errors instead of silently falling back to LoRA scanner when
  model root cannot be determined
- Scope .input-group CSS rules to modal IDs to fix style conflicts
  with download-modal.css
- Add i18n keys across all 10 locales with translations for
  zh-CN, zh-TW, ja, ko, de, es, fr, he, ru

py/routes/misc_route_registrar.py

@@ -103,6 +103,9 @@ MISC_ROUTE_DEFINITIONS: tuple[RouteDefinition, ...] = (
     RouteDefinition(
         "POST", "/api/lm/download-hf-model", "download_hf_model"
     ),
+    RouteDefinition(
+        "POST", "/api/lm/set-hf-url", "set_hf_url"
+    ),
     # Agent skill endpoints
     RouteDefinition(
         "GET", "/api/lm/agent/skills", "get_agent_skills"