feat: Implement cancellation of stale generations in the service and repository, along with a new test.

api/service/generation_service.py

@@ -460,4 +460,15 @@ class GenerationService:
             return True
         except Exception as e:
             logger.error(f"Error deleting generation {generation_id}: {e}")
-            return False
+            return False
+
+    async def cleanup_stale_generations(self):
+        """
+        Cancels generations that have been running for more than 1 hour.
+        """
+        try:
+            count = await self.dao.generations.cancel_stale_generations(timeout_minutes=60)
+            if count > 0:
+                logger.info(f"Cleaned up {count} stale generations (timeout)")
+        except Exception as e:
+            logger.error(f"Error cleaning up stale generations: {e}")