fix: playlist cover auto-refresh after upload

Re-generate coverUrl (includes fresh auth params) + append _cb=timestamp
to bypass browser cache. Update both detail view and edit modal preview.

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

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v36';
+const CACHE = 'ns-v37';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];