[AGENT] Polish desktop recorder UX with meters, icons, and hotkeys

[BASIC-BIT]

[AGENT]

Summary

Improve the desktop recorder UX now that the basic Windows recorder/upload path works.

Desired improvements

• Replace the default React/Tauri-style desktop app icon with Chronote-branded assets.
• Add mic and system/output volume meters so users can see capture is alive.
• Add a compact recorder window or mode focused only on start/stop/status.
• Add a hotkey to show/hide the recorder window.
• Consider a hotkey to start/stop recording, with safe confirmation or clear status to prevent accidental capture.
• Keep the local recorder UX distinct from any future full desktop portal shell.

Acceptance criteria

1. The desktop app uses Chronote-branded icons in the window and installer bundle.
2. The recorder UI shows live signal/volume for mic and system/output capture.
3. The UI clearly indicates when each source is silent, unavailable, or recording.
4. A compact recorder mode or design exists for low-friction capture.
5. Hotkey behavior is designed and implemented or explicitly deferred with a follow-up issue.
6. Desktop checks and screenshot/manual QA cover the updated recorder surface.