Agents window: Show confirmation after Commit and Sync actions complete

## Feature request

In the Agents window, after I click the **Commit** or **Sync** button in the title bar, the button disappears. I assume this means the action completed successfully, but there is no clear confirmation of the resulting state of my changes.

## Current behavior

1. Open an agent session with changes ready to commit or sync.
2. Click **Commit** or **Sync** in the title bar.
3. The button disappears without an explicit success confirmation or an indication of the new repository state.

The disappearing button indirectly suggests success, but leaves uncertainty about whether the action completed and what state the changes are now in.

## Suggested behavior

After either action completes, show clear confirmation and the resulting state—for example, a brief success message and/or persistent status indicating that changes are committed, synced, or up to date. Failures should remain clearly distinguishable from successful completion. This doesn't need to be in a modal or anything the user needs to interact with or dismiss, but perhaps inline?