agent_ui: Add more UI refinements to sidebar (#51545)

- Move archive button to the header for simplicity
- Hook up the delete button in the archive view
- Improve how titles are displayed before summary is generated
- Hook up keybinding for deleting threads in both the sidebar and
archive view

Release Notes:

- N/A
e79429b51bDanilo Leal committed on 3/14/2026, 5:14:25 AM· committed by GitHubparent80acfff
9 files changedLine totals unavailable