fix: remove unused agent arg from App.poll

tests/test_app.py

@@ -9,7 +9,7 @@ def test_app_facade_with_memory():
     t = app.create_thread(alice, bob)
     app.append(t.id, alice, "hello")
     assert app.has_unread(t.id, bob) is True
-    msgs = app.poll(t.id, bob)
+    msgs = app.poll(t.id)
     assert len(msgs) == 1
     app.mark_read(t.id, bob, msgs[0].seq)
     assert app.has_unread(t.id, bob) is False