Add PDF document service with AI extraction and per-app settings

- New `features/doc-service` FastAPI microservice: PDF upload, async
  text extraction (pdfplumber), AI classification via Anthropic/Ollama/
  LM Studio, per-user categories, file download
- Alembic migration isolated with `alembic_version_doc_service` table
- Main backend: httpx proxy routers for /api/documents/* and
  /api/documents/categories/*, admin settings API at /api/settings/*
- Runtime config in /config/doc_service_config.json (shared Docker
  volume); api_key masking on reads; atomic write with os.replace()
- Frontend: DocumentsPage, DocumentAdminSettingsPage, updated AppsPage
  launcher hub, simplified Nav (removed Settings link), new routes
- docker-compose: doc-service service, doc_data + app_config volumes,
  removed internal:true from backend-net for outbound AI API calls
- Fix pre-commit hook: probe Docker socket path so git subprocess picks
  up Docker Desktop on macOS
- Fix security_check.py: use sys.executable for bandit so venv python
  is used instead of system python

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

features/doc-service/app/deps.py

@@ -0,0 +1,12 @@
+from fastapi import Header, HTTPException
+
+
+async def get_user_id(x_user_id: str = Header(...)) -> str:
+    """
+    Extract the user identity injected by the main backend proxy.
+    The main backend validates the JWT and forwards the user ID via this header.
+    Doc-service trusts it because it is only reachable from backend on backend-net.
+    """
+    if not x_user_id:
+        raise HTTPException(status_code=400, detail="Missing X-User-Id header")
+    return x_user_id