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>

tests/test_mcp_endpoint.py

@@ -88,7 +88,11 @@ async def test_mcp_endpoint_valid_token_passes_auth():
     """With a valid Bearer, the request must successfully reach FastMCP's
     initialize handler. Asserting `!= 401` is too weak: it lets a 404 from
     a path-mismatch (the original bug) through. FastMCP responds 200 to a
-    well-formed initialize handshake."""
+    well-formed initialize handshake.
+
+    FastMCP's session manager normally starts via Quart's @before_serving
+    hook in production. This raw-ASGI test doesn't go through Quart's
+    serving lifecycle, so we manually enter the session manager."""
     fake_key = MagicMock()
     fake_key.user_id = 7
     fake_key.scope = "write"
@@ -101,19 +105,20 @@ async def test_mcp_endpoint_valid_token_passes_auth():
             "clientInfo": {"name": "test", "version": "0"},
         },
     }).encode()
-    with patch(
-        "fabledassistant.mcp.auth.lookup_key",
-        AsyncMock(return_value=fake_key),
-    ):
-        status, _ = await _send_request(
-            app, "POST", "/mcp",
-            headers={
-                "Authorization": "Bearer fmcp_valid",
-                "Content-Type": "application/json",
-                "Accept": "application/json, text/event-stream",
-            },
-            body=initialize_body,
-        )
+    async with app.mcp_instance.session_manager.run():
+        with patch(
+            "fabledassistant.mcp.auth.lookup_key",
+            AsyncMock(return_value=fake_key),
+        ):
+            status, _ = await _send_request(
+                app, "POST", "/mcp",
+                headers={
+                    "Authorization": "Bearer fmcp_valid",
+                    "Content-Type": "application/json",
+                    "Accept": "application/json, text/event-stream",
+                },
+                body=initialize_body,
+            )
     assert status == 200, f"expected 200 from FastMCP initialize, got {status}"