#389 fix(desktop): make error toast description readable in light mode

Summary

• Created ThemedToaster component that connects the app's theme store to sonner
• Error toast descriptions are now readable in light mode (previously had poor contrast with gray text on white background)

Test plan

• Open the desktop app in light mode
• Trigger an error toast (e.g., try to open a folder that's not a git repository from the workspace dropdown)
• Verify the toast description text is readable

🤖 Generated with Claude Code

Summary by CodeRabbit

• Improvements
  • Toast notifications now respect your app's theme preference, automatically adapting between light and dark modes for improved visual consistency.

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