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/doc-service/app/schemas/document.py

@@ -27,6 +27,13 @@ class DocumentOut(BaseModel):
     model_config = {"from_attributes": True}
 
 
+class DocumentPage(BaseModel):
+    items: list[DocumentOut]
+    total: int
+    page: int
+    pages: int
+
+
 class DocumentStatusOut(BaseModel):
     id: str
     status: str