feat(agent): add LLM-powered metadata enrichment system with AgentCLI and PostProcessor

Introduce an agent skill framework for LLM-driven metadata enrichment:

- AgentCLI (py/agent_cli/): in-process wrappers around internal services
  using standard relative imports, eliminating the need for sys.path hacks
- LLMService: centralized BYOK (bring-your-own-key) LLM client supporting
  OpenAI, Ollama, and custom OpenAI-compatible endpoints
- PostProcessor: deterministic engine that applies LLM output via AgentCLI
  (replaces old handler.py + _BASE_MODEL_ALIASES approach)
- SkillRegistry: filesystem-based skill discovery (skill.yaml + prompt.md)
- AgentService: orchestrates skill execution with WebSocket progress
- Frontend AgentManager: WebSocket listeners, skill execution, config UI
- Context menu entries (single + bulk) for "Enrich Metadata (Agent)"
- Settings UI for AI Provider configuration (BYOK)
- Full i18n support across 9 locales

Bug fixes found during review:
- aiohttp.web.json_response: status_code= -> status=
- settings_modal cancelEditApiKey: wrong argument position
- AgentManager.isLlmConfigured: allow Ollama without API key
- PostProcessor._merge_tags: lowercase all tags to match TagUpdateService

templates/components/context_menu.html

@@ -12,6 +12,9 @@
     <div class="context-menu-item" data-action="check-updates">
         <i class="fas fa-bell"></i> <span>{{ t('loras.contextMenu.checkUpdates') }}</span>
     </div>
+    <div class="context-menu-item" data-action="enrich-hf-agent">
+        <i class="fas fa-wand-magic-sparkles"></i> <span>{{ t('loras.contextMenu.enrichHfAgent') }}</span>
+    </div>
     <div class="context-menu-item" data-action="relink-civitai">
         <i class="fas fa-link"></i> <span>{{ t('loras.contextMenu.relinkCivitai') }}</span>
     </div>
@@ -83,6 +86,9 @@
         <div class="context-menu-item" data-action="resume-metadata-refresh">
             <i class="fas fa-redo"></i> <span>{{ t('loras.bulkOperations.resumeMetadataRefresh') }}</span>
         </div>
+        <div class="context-menu-item" data-action="enrich-hf-agent-bulk">
+            <i class="fas fa-wand-magic-sparkles"></i> <span>{{ t('loras.bulkOperations.enrichHfAgent') }}</span>
+        </div>
     </div>
     <div class="context-menu-section" data-section="workflow">
         <div class="context-menu-section-header">{{ t('loras.bulkOperations.sections.workflow') }}</div>