[desktop] Document cursor preference handling in AGENTS guide

[Codex]

AGENTS.md was missing the new cursor preference details and associated menu event, leaving setup docs incomplete.

• Docs: Note cursor as a persisted localStorage key alongside other appearance settings.
• Events: Describe the cursor_change menu→frontend event with other preference signals.

Example snippet:

- All persistence via `localStorage` (key: `rootDir`, `font`, `size`, `appearance`, `cursor`).
- `font_change` / `size_change` / `appearance_change` / `cursor_change` → update preferences

Greptile Summary

This PR updates the AGENTS.md documentation to accurately reflect the cursor preference feature added in PR #13. Two lines were modified to include the new cursor localStorage key and the cursor_change event handler, keeping the documentation in sync with the current codebase implementation.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• Documentation-only change that accurately reflects existing implementation with no code modifications
• No files require special attention

Important Files Changed

Filename	Overview
AGENTS.md	Documentation updated to reflect new cursor localStorage key and cursor_change event

_{Last reviewed commit: 12bf5e7}