feat(desktop): Add command to /toggle-appearence

[dbpolito]

Add a way to use /toggle-appearance, while we don't have a command pallet like TUI, this is fine.

One thing i notice is this keybind mod+shift+s only works on home, because when you're on a session, there is another keybind for opening a new session, which takes precedence.

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

Related PR Found:

• PR feat(tui): add appearance setting with dark/light/system modes #7182: feat(tui): add appearance setting with dark/light/system modes
  • This PR adds appearance/theme toggle functionality to the TUI (terminal UI), which is related to the desktop version's toggle-appearance command being added in PR feat(desktop): Add command to /toggle-appearence #8239. Both are addressing similar appearance/theme toggle functionality across different interfaces.

The other results (PR #6291 on desktop themes docs and PR #7290 on i18n) are less directly related to the toggle-appearance functionality.