fix: reject malformed activity feed payloads (#107)

src/gitea_proxy.py

@@ -40,6 +40,10 @@ async def pull_requests() -> list[dict]:
 async def activity_events() -> list[dict]:
     user = await current_user()
     events = await fetch(f"users/{user['login']}/activities/feeds?limit=20")
+    if events is None:
+        events = []
+    elif not isinstance(events, list):
+        raise ValueError("Gitea activity feed response was not a list")
     return [
         {
             "type": (