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>

CLAUDE.md

@@ -88,6 +88,56 @@ Browser → Vite dev server (:5173)
 2. Token stored in `localStorage`, attached to every request by the Axios interceptor
 3. Protected routes call `GET /api/users/me`; `get_current_user` dep validates the token on the server
 
+## STATUS.md workflow
+
+Every directory that contains runnable code, a feature service, or significant logic has a `STATUS.md` file. These files are the canonical **resume point** for development — they describe what the component is, what it currently does, its limitations, and what is planned next.
+
+### At the start of every conversation
+
+1. Read the `STATUS.md` for every directory you will touch.
+2. If the file does not yet exist for a directory you are working in, create one using the structure below.
+
+This applies equally to subagents — always read the relevant `STATUS.md` before starting work.
+
+### After making changes
+
+Update any `STATUS.md` that is affected:
+- Add new endpoints / models / routes to the **Current functionality** tables.
+- Move completed items off the **Future work** checklist.
+- Add new items to **Known limitations** or **Future work** as appropriate.
+- Keep the **What it is** summary accurate (port, DB, storage, etc.).
+
+### STATUS.md structure
+
+Each file must contain these sections (add/remove sub-sections as needed):
+
+```markdown
+# <Service Name> — Status
+
+## What it is
+One paragraph: purpose, internal port, database/storage, how traffic arrives.
+
+## Current functionality
+Subsections per router / feature area. Use tables for endpoints.
+
+## Architecture
+ASCII diagram showing the call graph / data flow.
+
+## Known limitations / not implemented
+Bullet list of gaps that are known but not yet addressed.
+
+## Future work
+- [ ] Checklist of planned improvements
+```
+
+Root-level services and directories to maintain STATUS.md in:
+- `backend/` — FastAPI gateway
+- `features/ai-service/` — AI intermediary
+- `features/doc-service/` — document microservice
+- `frontend/` — React SPA
+
+---
+
 ## Git convention
 
 Always run `git push` immediately after every `git commit`.