fix(ui): stop accidental text-selection of UI chrome when dragging near controls

Dragging the mouse near a field edge (Global Suche, the importer, etc.) started
a text selection of the surrounding page titles/labels instead of feeling like an
app. Disable user-select on the #app shell; re-enable it for real text fields
(input/textarea/contenteditable) and copyable content (lyrics). Setup screen is
outside #app and unaffected. SW cache -> ns-v66.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v65';
+const CACHE = 'ns-v66';
 const PRECACHE = ['/', 'index.html', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];
 // Auth token params stripped from cache keys so artwork survives across sessions/token refreshes.