feat(ui): copy song fields from song info via double-click

Double-click the Title, Artist, or Album value to copy plain text to the
clipboard with toast feedback. Apply user-select: none on those cells so
double-click does not trigger word selection.

src/styles/components.css

@@ -1394,6 +1394,11 @@
   padding: 4px 16px 4px 8px;
   word-break: break-all;
 }
+/* Double-click copies; avoid browser selecting word on dblclick */
+.song-info-value--no-select {
+  user-select: none;
+  -webkit-user-select: none;
+}
 .song-info-divider {
   padding: 6px 0;
   border-bottom: 1px solid var(--border-subtle);