Desk Rave v0.1.2

0.1.2: fullscreen + launch-on-boot toggles, QR moved right

Desktop-app appliance controls (great for the Pi kiosk migration):
- "Start in fullscreen" + "Launch on startup" toggles in first-run setup
  AND Settings; applied immediately and re-applied at boot.
- Adds tauri-plugin-autostart; fullscreen via the window API. Both are
  DESKTOP-only (dynamically imported -> code-split out of the web/itch
  bundle; the toggles are hidden entirely on web).
- QR button moved to the top-right corner (was crowding the bonuses/
  unlocks panel top-left). Kiosk-only UI (hidden in standalone).

Verified: tsc + cargo check + build:itch all clean; web hides the toggles
and shows no errors; QR renders top-right.

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