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/app.py

@@ -446,7 +446,7 @@ async def app_lifespan_basic(server: FastMCP) -> AsyncIterator[AppContext]:
         # Start background tasks using anyio TaskGroup
         async with anyio.create_task_group() as tg:
             # Start scanner task
-            tg.start_soon(
+            await tg.start(
                 scanner_task,
                 send_stream,
                 shutdown_event,
@@ -457,7 +457,7 @@ async def app_lifespan_basic(server: FastMCP) -> AsyncIterator[AppContext]:
 
             # Start processor pool (each gets a cloned receive stream)
             for i in range(settings.vector_sync_processor_workers):
-                tg.start_soon(
+                await tg.start(
                     processor_task,
                     i,
                     receive_stream.clone(),
@@ -1147,7 +1147,7 @@ def get_app(transport: str = "sse", enabled_apps: list[str] | None = None):
                 # Start background tasks using anyio TaskGroup
                 async with anyio_module.create_task_group() as tg:
                     # Start scanner task
-                    tg.start_soon(
+                    await tg.start(
                         scanner_task,
                         send_stream,
                         shutdown_event,
@@ -1158,7 +1158,7 @@ def get_app(transport: str = "sse", enabled_apps: list[str] | None = None):
 
                     # Start processor pool (each gets a cloned receive stream)
                     for i in range(settings.vector_sync_processor_workers):
-                        tg.start_soon(
+                        await tg.start(
                             processor_task,
                             i,
                             receive_stream.clone(),