fix: playlist cover upload — send raw image body not multipart

Navidrome expects Content-Type: image/* with raw binary body.
Bump SW to ns-v34.

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

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v33';
+const CACHE = 'ns-v34';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];