fix: normalize null activity feed payloads (#93)

src/gitea_proxy.py

@@ -47,6 +47,6 @@ async def activity_events() -> list[dict]:
             "repo": event.get("repo") or {},
             "created_at": event.get("created", ""),
         }
-        for event in events
+        for event in (events or [])
         if isinstance(event, dict)
     ]