docs: Improve content in /ai/agent-panel and /ai/rules (#42055)

- Clarify about first-party supported features in external agents
- Create new section for selection as context for higher visibility
- Add keybindings for agent profiles
- Fix outdated setting using `assistant` instead of `agent`
- Add keybinding for accessing the rules library

Release Notes:

- N/A
69862790cbDanilo Leal committed on 11/6/2025, 4:18:55 AM· committed by GitHubparent284d8f7
2 files changedLine totals unavailable