fix: clip bar no longer visible before any clip has played

The author rule #clip-bar{display:flex} overrides the UA stylesheet's
[hidden]{display:none}, so the hidden attribute toggled by playClip()/
hideClipBar() had no visual effect: the bar rendered from page load and
the close button appeared to do nothing. Restate display:none for the
hidden state.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

webui.html

@@ -125,6 +125,9 @@ svg.day-timeline{display:block;width:100%;height:22px}
 #clip-bar{position:fixed;bottom:0;left:0;right:0;z-index:20;background:var(--surf);
   border-top:1px solid var(--brd);padding:8px 28px;display:flex;align-items:center;
   gap:10px;flex-wrap:wrap}
+/* display:flex above beats the UA's [hidden]{display:none} — restate it, or
+   the bar is visible from page load and the close button looks dead */
+#clip-bar[hidden]{display:none}
 #clip-bar audio{flex:1 1 240px;min-width:180px;height:32px}
 #clip-label{font-size:12px;color:var(--muted);font-family:ui-monospace,monospace;
   white-space:nowrap;overflow:hidden;text-overflow:ellipsis;max-width:38%}