threads: order topic chips newest-first beneath General

The gateway already stored a created timestamp per channel/thread but
never sent it over the wire. Now:

- protocol.py: _channel_payload() includes created (unix seconds)
- Protocol.kt: ChannelInfo.created (default 0.0 for legacy gateways)
- ChatScreen: topic switcher sorts threads created-desc (newest right
  after General, swipe new -> old), name as tie-break
- frames.schema.json: document the created field
- ChannelCreatedWireTest: wire deserialization + ordering tests

gateway-plugin/protocol.py

@@ -559,6 +559,8 @@ def _channel_payload(entry: dict[str, Any]) -> dict[str, Any]:
     }
     if entry.get("parent_chat_id") is not None:
         payload["parent_chat_id"] = entry["parent_chat_id"]
+    if entry.get("created"):
+        payload["created"] = entry["created"]
     if entry.get("is_default"):
         payload["is_default"] = True
     if entry.get("archived"):