feat: playback overlay with seek bar, auto-hide and double-tap skip (v0.3.4)

New PlaybackOverlay component replaces the old hint bar in ChannelScreen.
The overlay sits as a fullscreen layer above the app during playback:

- Auto-hides after 5 s while playing; stays visible when paused;
  reactivated by any gamepad key press or mouse movement
- Center play/pause button, channel avatar, title, LIVE badge
- VOD: seek bar with pointer-capture scrubbing, current time / total duration
- Live: pulsing LIVE indicator instead of seek bar
- Double-tap zones left/right (±10 s) with animated skip feedback
- Gamepad hints in the top bar
- New icons: PlayIcon, PauseIcon, StopIcon in Icons.tsx
- New IPC channel `playback:time-update` (~1 Hz) pushes absolute playback
  position from main process to renderer; adds PlaybackTimeUpdate type
  and onTimeUpdate bridge in preload + t4sd.d.ts
- PlaybackEvent extended with durationSeconds and isLive fields

package.json

@@ -1,7 +1,7 @@
 {
   "name": "twitch4steamdeck",
-  "version": "0.3.3",
-  "description": "Werbefreier Twitch-Client für das Steam Deck (Live & VOD, Big-Screen-UI)",
+  "version": "0.3.4",
+  "description": "Twitch-Client für das Steam Deck (Live & VOD, Big-Screen-UI)",
   "main": "out/main/index.js",
   "author": "twitch4steamdeck",
   "license": "MIT",