feat: smooth progress bar scrubbing with touch drag support

- initProgressScrub() adds touchstart/move/end + mousedown drag to both
  the player bar and NP overlay progress bars
- CSS transition disabled during scrub so fill follows finger instantly
- updateProgress() skips DOM updates while _scrubbing is active so
  timeupdate events don't fight the drag position
- Works on both bars with a shared _initBarScrub helper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v24';
+const CACHE = 'ns-v25';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];