fix: playlist cover upload — POST /api/playlist/{id}/image FormData with JWT

Confirmed endpoint pattern from Navidrome API contract (artist/:id/image).
FormData field 'image' + X-Nd-Authorization Bearer token. Bump SW ns-v36.

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

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v35';
+const CACHE = 'ns-v36';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];