jbot: fix voice button visibility - chat-panel height overflow

.chat-panel was using height:100% which consumed all right-col space,
pushing VoiceButton out of view (clipped by overflow:hidden).

Fix: switch .chat-panel to flex:1 + min-height:0 so it participates
in flex layout and leaves room for the VoiceButton below it.

Also moved VoiceButton component outside App() to avoid React
component-identity churn on every render.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

static_src/jbot/App.css

@@ -272,7 +272,8 @@ kbd {
 .chat-panel {
   display: flex;
   flex-direction: column;
-  height: 100%;
+  flex: 1;
+  min-height: 0;
   padding: 14px 18px;
   gap: 10px;
   overflow: hidden;

static_src/jbot/App.jsx

@@ -45,41 +45,39 @@ function speakText(text) {
   });
 }
 
+// ── Hold-to-talk voice button (defined outside App to keep stable identity) ──
+function VoiceButton({ phase, onStart, onEnd }) {
+  const busy = phase === 'thinking' || phase === 'speaking';
+  let label = '🎙 按住说话';
+  let mod   = '';
+  if (phase === 'acquiring')      { label = '⏳ 准备中…';  mod = ' vbtn--acquiring'; }
+  else if (phase === 'listening') { label = '🔴 松开发送'; mod = ' vbtn--recording'; }
+  else if (phase === 'thinking')  { label = '⚙ 思考中…';  mod = ' vbtn--busy'; }
+  else if (phase === 'speaking')  { label = '🔊 播放中…';  mod = ' vbtn--busy'; }
+
+  const startEvt = (e) => { e.preventDefault(); if (!busy) onStart(); };
+  const endEvt   = (e) => { e.preventDefault(); onEnd(); };
+
+  return (
+    <div className="vbtn-wrap">
+      <button
+        className={`vbtn${mod}`}
+        disabled={busy}
+        onMouseDown={startEvt}
+        onMouseUp={endEvt}
+        onMouseLeave={endEvt}
+        onTouchStart={startEvt}
+        onTouchEnd={endEvt}
+        onTouchCancel={endEvt}
+      >
+        {label}
+      </button>
+    </div>
+  );
+}
+
 export default function App() {
   const navigate = useNavigate();
-
-  // ── VoiceButton: WeChat-style hold-to-record ──────────────
-  // Placed here so it shares App's handleSpaceDown/handleSpaceUp via closure.
-  function VoiceButton({ phase, onStart, onEnd }) {
-    const busy = phase === 'thinking' || phase === 'speaking';
-    let label = '🎙 按住说话';
-    let mod   = '';
-    if (phase === 'acquiring') { label = '⏳ 准备中…';  mod = ' vbtn--acquiring'; }
-    else if (phase === 'listening') { label = '🔴 松开发送'; mod = ' vbtn--recording'; }
-    else if (phase === 'thinking')  { label = '⚙ 思考中…'; mod = ' vbtn--busy'; }
-    else if (phase === 'speaking')  { label = '🔊 播放中…'; mod = ' vbtn--busy'; }
-
-    const startEvt = (e) => { e.preventDefault(); if (!busy) onStart(); };
-    const endEvt   = (e) => { e.preventDefault(); onEnd(); };
-
-    return (
-      <div className="vbtn-wrap">
-        <button
-          className={`vbtn${mod}`}
-          disabled={busy}
-          onMouseDown={startEvt}
-          onMouseUp={endEvt}
-          onMouseLeave={endEvt}
-          onTouchStart={startEvt}
-          onTouchEnd={endEvt}
-          onTouchCancel={endEvt}
-        >
-          {label}
-        </button>
-      </div>
-    );
-  }
-
   // ── Expression / auto-rotate state ───────────────────────────
   const [exprId,     setExprId]     = useState(ALL_AUTO_IDS[0]);
   const [autoRotate, setAutoRotate] = useState(true);