Fix command palette theme toggle to use NavbarContext

[aayan-rashid]

Summary

This PR updates the Command Palette theme toggle to use the shared NavbarContext instead of directly manipulating the DOM and localStorage.

Changes

• Replaced direct theme manipulation with useNavbar().setTheme().
• Removed duplicate theme management logic from CommandPalette.
• Ensures all components consuming NavbarContext remain synchronized after toggling the theme.

Testing

• Verified the project runs successfully with npm run dev.
• Verified all existing tests pass (27/27).
• Confirmed the theme toggles correctly through the Command Palette and stays synchronized with the navbar theme toggle.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.