Add priority queue to ai-service and STATUS.md workflow

- Introduce async priority queue service in ai-service; all /chat calls now route through it
- Refactor chat router to separate execute_chat (core logic) from the HTTP handler
- Add /queue endpoints (status, pause, resume, cancel) for queue management
- Update ai-service config to use Pydantic v2 model_config style
- Add STATUS.md files for backend, ai-service, doc-service, and frontend
- Document STATUS.md workflow in CLAUDE.md
- Update doc-service documents router and schemas; frontend DocumentsPage and API client

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

features/ai-service/app/core/config.py

@@ -5,8 +5,7 @@ class Settings(BaseSettings):
     PROJECT_NAME: str = "ai-service"
     CONFIG_PATH: str = "/config/ai_service_config.json"
 
-    class Config:
-        env_file = ".env"
+    model_config = {"env_file": ".env", "extra": "ignore"}
 
 
 settings = Settings()