fix(events): restore exc_info=True in handler error logging

The exc_info=True parameter was accidentally removed from the
event_handler_failed logging block during a previous formatting cleanup.
This restores it to include full exception tracebacks in warning logs,
which is required by existing integration tests.

Refs: #10378

src/cleveragents/infrastructure/events/reactive.py

@@ -145,6 +145,7 @@ class ReactiveEventBus:
                     handler=getattr(handler, "__qualname__", repr(handler)),
                     error_type=type(exc).__name__,
                     error=str(exc),
+                    exc_info=True,
                 )
 
     def subscribe(