fix: system theme

[RohitKushvaha01]

Closes #2521

[greptile-apps]

Greptile Summary

This PR switches system-theme synchronization to browser color-scheme events. The main changes are:

• Replaces periodic theme polling with a MediaQueryList change listener.
• Applies the preferred editor theme when the OS color scheme changes.

Confidence Score: 5/5

The changed flow looks mergeable after two small compatibility and notification fixes.

• Older MediaQueryList implementations can fail when the watcher starts.
• Automatic OS theme changes can display a misleading settings-saved toast.
• Listener registration and removal otherwise use the same stable callback.

src/palettes/changeTheme/index.js and src/theme/preInstalled.js

Important Files Changed

Filename	Overview
src/palettes/changeTheme/index.js	Replaces polling with a MediaQueryList listener, but lacks the legacy listener fallback.
src/theme/preInstalled.js	Synchronizes the editor theme with the OS theme, but enables save notifications for automatic updates.

_{Reviews (1): Last reviewed commit: "fix: system theme" | Re-trigger Greptile}