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>

styles.css

@@ -14,6 +14,11 @@
 }
 *,*::before,*::after{box-sizing:border-box;margin:0;padding:0;-webkit-tap-highlight-color:transparent}
 *:focus{outline:none}
+/* App-like feel: dragging near controls must not accidentally select UI chrome
+   (page titles, labels, buttons). Real text fields and copyable content opt back in. */
+#app{-webkit-user-select:none;user-select:none}
+#app input,#app textarea,#app [contenteditable=true],#app .selectable,
+#app #np-lyrics-content,#app .lyrics-line,#app .lyrics-plain{-webkit-user-select:text;user-select:text}
 html,body{height:100%;font-family:var(--font);background:var(--bg);color:var(--text);overflow:hidden}
 ::-webkit-scrollbar{width:4px}::-webkit-scrollbar-track{background:transparent}::-webkit-scrollbar-thumb{background:var(--surface2);border-radius:2px}