chore(api): enhance exception handing in BaseSession

Replace `Exception` with more specific error `concurrent.futures.TimeoutError`.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

api/core/mcp/session/base_session.py

@@ -194,7 +194,7 @@ class BaseSession(
         if self._receiver_future:
             try:
                 self._receiver_future.result(timeout=5.0)  # Wait up to 5 seconds
-            except Exception:
+            except concurrent.futures.TimeoutError:
                 # If the receiver loop is still running after timeout, we'll force shutdown
                 pass