fix: integrate vector sync tasks with Starlette lifespan for streamable-http

Fixes background task startup for streamable-http transport by integrating
vector sync initialization into the Starlette lifespan context manager.

Starlette Lifespan Integration:
- Moved background task startup from FastMCP lifespan to Starlette lifespan
- FastMCP lifespan only triggers on MCP session establishment
- Starlette lifespan runs on server startup (correct timing)
- Fixed module scoping issues with local imports (anyio_module, asyncio_module)
- Added conditional startup based on oauth_enabled flag

Scanner Fixes:
- Fixed NotesClient method: list_notes() → get_all_notes()
- Properly handle AsyncIterator with list comprehension
- Collects all notes before processing

Verified Working:
- Background tasks start successfully on server startup
- Scanner fetches notes from Nextcloud API
- Processor pool (3 workers) ready for document processing
- Health endpoint reports Qdrant status
- No startup errors

Phase 3 Complete:
- BasicAuth mode with vector sync fully functional
- Background tasks integrate cleanly with streamable-http transport
- Graceful shutdown with coordinated task cancellation

Related: ADR-007 Background Vector Database Synchronization

🤖 Generated with Claude Code (https://claude.com/claude-code)

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

nextcloud_mcp_server/vector/scanner.py

@@ -92,7 +92,7 @@ async def scan_user_documents(
     logger.info(f"Scanning documents for user: {user_id}")
 
     # Fetch all notes from Nextcloud
-    notes = await nc_client.notes.list_notes()
+    notes = [note async for note in nc_client.notes.get_all_notes()]
     logger.debug(f"Found {len(notes)} notes for {user_id}")
 
     if initial_sync: