fix(mcp): start FastMCP session manager via Quart serving lifecycle

After fixing the /mcp path forwarding in 1fd303a, requests now reach
FastMCP — but its StreamableHTTPSessionManager raises:

  RuntimeError: Task group is not initialized. Make sure to use run().

The session manager owns a task group that must be running before it
can handle requests. In a stand-alone Starlette app this happens via
the `lifespan` parameter (lifespan = session_manager.run). Hosted
inside Quart, my dispatch wrapper only forwards HTTP events, not
lifespan, so the manager never got its startup signal.

Fix: hook session_manager.run() (an async context manager) into
Quart's @app.before_serving and @app.after_serving so the task group
is alive across the serving window.

The CI integration test was hitting the same crash because it drives
app.asgi_app raw without going through Quart's serving lifecycle —
@before_serving never fires. Updated the test to manually enter
session_manager.run() around the request.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/fabledassistant/mcp/server.py

@@ -36,7 +36,13 @@ def mount_mcp(app: Quart) -> None:
     A small ASGI middleware between Quart and the FastMCP sub-app validates the
     Bearer token against the api_keys table. Authenticated requests have their
     user_id attached to the ASGI scope under "scribe_user_id" for tool handlers
-    to read in later phases.
+    to read.
+
+    FastMCP's streamable_http session manager owns a task group that must be
+    running before it can serve requests. In a stand-alone Starlette deployment
+    that would happen via the Starlette `lifespan` parameter. Since we're hosted
+    inside Quart, we hook the session manager's `run()` async context manager
+    into Quart's serving lifecycle (before_serving / after_serving).
     """
     from fabledassistant.mcp.auth import resolve_bearer_to_user_id
 
@@ -44,6 +50,18 @@ def mount_mcp(app: Quart) -> None:
     mcp_asgi = mcp.streamable_http_app()
     app.mcp_instance = mcp
 
+    @app.before_serving
+    async def _start_mcp_session() -> None:
+        cm = mcp.session_manager.run()
+        await cm.__aenter__()
+        app._mcp_session_cm = cm
+
+    @app.after_serving
+    async def _stop_mcp_session() -> None:
+        cm = getattr(app, "_mcp_session_cm", None)
+        if cm is not None:
+            await cm.__aexit__(None, None, None)
+
     async def auth_wrapped(scope, receive, send):
         if scope["type"] != "http":
             return await mcp_asgi(scope, receive, send)