Problem

The auto-updater installs new versions silently. Users don't learn about new features (Ghost Mode, Quick-Clip, multi-pane, dark mode) unless they happen to check the README.

Proposed approach

• Compare the launched app version to the last-shown version stored in settings.
• If different, show a non-blocking modal listing what's new (read from a bundled JSON or hardcoded array per version).
• "Got it" dismisses + writes the new version to settings.

Files to touch

• New: `src/whats-new.json` (per-version highlights)
• `src/settings.js` — `lastShownVersion` key
• `src/renderer.js` — modal + check on launch

Acceptance criteria

• First launch on a new version shows the modal once.
• Subsequent launches of the same version don't.