Show app version in sidebar, make the sidebar collapsible, and add a Light/Dark/Auto theme switch

- Expose the AeroFetch version over IPC (app:version → app.getVersion); the
  sidebar brand now shows "v<version>" beneath the name.
- Sidebar can collapse to a 60px icon-only rail via a toggle button; nav items
  and the theme control fall back to icon + tooltip when collapsed. The state is
  persisted in localStorage so it survives restarts. Hint gains left/right
  placements for the collapsed-rail tooltips.
- Replace the binary dark-mode Switch with an explicit 3-way Light / Dark / Auto
  segmented control (Auto follows the OS). Collapsed, it becomes a single button
  that cycles the three modes.
- Bump version to 0.3.2.

Verified in the browser UI preview: version label, collapse/expand, dark mode,
and the theme switch all render correctly with no console errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/shared/ipc.ts

@@ -4,6 +4,8 @@
  */
 
 export const IpcChannels = {
+  /** the AeroFetch app version (package.json / app.getVersion) */
+  appVersion: 'app:version',
   ytdlpVersion: 'ytdlp:version',
   probe: 'media:probe',
   downloadStart: 'download:start',