fix: Navidrome REST auth for playlist cover — use JWT Bearer token

POST /auth/login to get JWT token, then X-Nd-Authorization: Bearer <token>
for cover upload/delete. Resets cached token on auth failure.
Bump SW to ns-v32.

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

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v31';
+const CACHE = 'ns-v32';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];