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/handlers/misc_handlers.py

@@ -3448,6 +3448,7 @@ class MiscHandlerSet:
             # Hugging Face handlers
             "get_hf_repo_files": self.hf_handler.get_hf_repo_files,
             "download_hf_model": self.hf_handler.download_hf_model,
+            "set_hf_url": self.hf_handler.set_hf_url,
             # Agent skill handlers
             "get_agent_skills": self.agent_handler.get_agent_skills,
             "execute_agent_skill": self.agent_handler.execute_agent_skill,