The `/chats/{chat}/diff-status` endpoint was redundant because:
- The `Chat` type already has a `DiffStatus` field
- Listing chats already resolves and returns `diff_status`
- The `getChat` endpoint was the only one not resolving it (passing
`nil`)
## Changes
**Backend:**
- `getChat` now calls `resolveChatDiffStatus` and includes the result in
the response
- Removed `getChatDiffStatus` handler, route (`GET /diff-status`), and
SDK method
- Tests updated to use `GetChat` instead of `GetChatDiffStatus`
**Frontend:**
- `AgentDetail.tsx`: uses `chatQuery.data?.diff_status` instead of
separate query
- `RemoteDiffPanel.tsx`: accepts `diffStatus` as a prop instead of
fetching internally
- `AgentsPage.tsx`: `diff_status_change` events now invalidate the chat
query
- Removed `chatDiffStatus` query, `chatDiffStatusKey`, and
`getChatDiffStatus` API method
Kyle Carberry
27cbf5474b