refactor: migrate asyncio to anyio for consistent structured concurrency

Replace asyncio primitives with anyio equivalents throughout the codebase
to establish a single async pattern. This provides better structured
concurrency with automatic cancellation on errors and aligns with the
pytest anyio configuration.

Changes:
- hybrid.py: Replace asyncio.gather() with anyio task groups
- token_broker.py: Replace asyncio.Lock() with anyio.Lock()
- storage.py: Replace asyncio.run() with anyio.run()
- app.py: Replace tg.start_soon() with await tg.start() for task status
- processor.py: Add task_status parameter for structured startup
- scanner.py: Add task_status parameter for structured startup
- CLAUDE.md: Update async/await patterns guidance

The change from start_soon() to await tg.start() enables proper task
initialization signaling, ensuring background tasks are ready before
proceeding. This follows anyio best practices for structured concurrency.

All 118 unit tests pass with the new implementation.

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

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

nextcloud_mcp_server/auth/storage.py

@@ -1310,7 +1310,7 @@ async def generate_encryption_key() -> str:
 
 # Example usage
 if __name__ == "__main__":
-    import asyncio
+    import anyio
 
     async def main():
         # Generate a key for testing
@@ -1318,4 +1318,4 @@ if __name__ == "__main__":
         print(f"Generated encryption key: {key}")
         print(f"Set this in your environment: export TOKEN_ENCRYPTION_KEY='{key}'")
 
-    asyncio.run(main())
+    anyio.run(main)

nextcloud_mcp_server/auth/token_broker.py

@@ -14,11 +14,11 @@ The Token Broker provides:
 - Session vs background token separation (RFC 8693)
 """
 
-import asyncio
 import logging
 from datetime import datetime, timedelta, timezone
 from typing import Dict, Optional, Tuple
 
+import anyio
 import httpx
 import jwt
 from cryptography.fernet import Fernet
@@ -43,7 +43,7 @@ class TokenCache:
         self._cache: Dict[str, Tuple[str, datetime]] = {}
         self._ttl = timedelta(seconds=ttl_seconds)
         self._early_refresh = timedelta(seconds=early_refresh_seconds)
-        self._lock = asyncio.Lock()
+        self._lock = anyio.Lock()
 
     async def get(self, user_id: str) -> Optional[str]:
         """Get cached token if valid."""