feat: integrate Opus codec into lib/libopus + voice messages in chatgui

- Add lib/libopus/ (opus v1.6.1 embedded source: CELT 18 .c, SILK 77 .c, SILK float 28 .c, OPUS core 14 .c)
- Add lib/opus_codec.h/.c (wrapper: encoder, decoder, raw PCM int16)
- Add tests/test_opus_codec.c (7 tests: silence, sine, compression, PLC, null, defaults, multi-frame)
- chatgui: AudioRecorder (miniaudio capture, 48kHz mono)
- chatgui: VoiceEncoder (PCM→Opus file with custom container)
- chatgui: VoicePlayer (Opus→PCM playback via SoundManager)
- chatgui: PTT button in InputBar, voice message send/receive in MessageList
- chatgui: AudioDeviceSettingsPage (device selection, persisted in ui_state)
- chatgui: MessageDelegate voice message rendering (play button + duration)
- Update autotools: configure.ac, Makefile.am, src/Makefile.am, tests/Makefile.am
- Update CMake: chatgui CMakeLists.txt, libutun CMakeLists.txt (link libopus_internal.a)

tools/chatgui/src/messagedelegate.cpp

@@ -67,6 +67,35 @@ MessageDelegate::Layout MessageDelegate::calcLayout(
     QString text  = index.data(MsgTextRole).toString();
     L.isOutgoing = index.data(MsgIsOutgoingRole).toBool();
 
+    /* Voice message detection */
+    QString contentType = index.data(MsgContentTypeRole).toString();
+    L.isVoice = (contentType == "audio/opus");
+    if (L.isVoice) {
+        L.voiceDuration = index.data(MsgVoiceDurationRole).toString();
+        QFontMetrics fm(option.font);
+        int lineH = fm.lineSpacing();
+        L.totalHeight = qMax(lineH * 2 + kGap * 2, kAvatar) + kItemGap;
+        L.bubbleWidth = 160;
+        int contentEdge = L.isOutgoing
+            ? L.viewWidth - (L.narrow ? kMarginH : (kMarginH + kAvatar + kGap))
+            : (L.narrow ? kMarginH : (kMarginH + kAvatar + kGap));
+        if (!L.isOutgoing)
+            L.bubbleRect = QRect(contentEdge, 0, L.bubbleWidth, L.totalHeight - kItemGap);
+        else
+            L.bubbleRect = QRect(contentEdge - L.bubbleWidth, 0, L.bubbleWidth, L.totalHeight - kItemGap);
+        L.voicePlayBtnRect = QRect(L.bubbleRect.left() + kPadH, L.bubbleRect.top() + kPadTop + 4, 28, 28);
+        L.voiceDurationRect = QRect(L.bubbleRect.left() + kPadH + 36, L.bubbleRect.top() + kPadTop + 4,
+                                     L.bubbleWidth - kPadH * 2 - 36, 28);
+        if (!L.narrow) {
+            int avatarY = L.bubbleRect.bottom() - kAvatar;
+            if (!L.isOutgoing)
+                L.avatarRect = QRect(kMarginH, avatarY, kAvatar, kAvatar);
+            else
+                L.avatarRect = QRect(L.viewWidth - kMarginH - kAvatar, avatarY, kAvatar, kAvatar);
+        }
+        return L;
+    }
+
     L.emojiCount = detectEmojiOnly(text);
     L.emojiOnly = (L.emojiCount >= 1);
 
@@ -449,6 +478,43 @@ void MessageDelegate::paint(QPainter *painter, const QStyleOptionViewItem &optio
         return;
     }
 
+    if (L.isVoice) {
+        drawBubble(painter, L, option);
+        if (!L.narrow) drawAvatar(painter, L, index);
+
+        /* Play button */
+        painter->setPen(Qt::NoPen);
+        painter->setBrush(QColor(0x33, 0x90, 0xEC));
+        QPainterPath playPath;
+        QRectF playR = L.voicePlayBtnRect;
+        qreal cx = playR.center().x() - playR.width() / 6.0;
+        qreal cy = playR.center().y();
+        qreal hs = playR.height() / 2.5;
+        playPath.moveTo(cx, cy - hs);
+        playPath.lineTo(cx + hs * 1.5, cy);
+        playPath.lineTo(cx, cy + hs);
+        playPath.closeSubpath();
+        painter->drawPath(playPath);
+
+        /* Duration text */
+        painter->setPen(option.palette.text().color());
+        painter->setFont(option.font);
+        if (!L.voiceDuration.isEmpty())
+            painter->drawText(L.voiceDurationRect, Qt::AlignLeft | Qt::AlignVCenter, L.voiceDuration);
+
+        /* Time */
+        QFont timeFont = option.font;
+        timeFont.setPointSize(timeFont.pointSize() - 1);
+        painter->setFont(timeFont);
+        painter->setPen(option.palette.text().color().lighter(150));
+        QString timeStr = index.data(MsgTimeRole).toString();
+        QRect timeR = QRect(L.bubbleRect.right() - kPadH - 50, L.voicePlayBtnRect.bottom() + 4, 50, 16);
+        painter->drawText(timeR, Qt::AlignRight | Qt::AlignVCenter, timeStr);
+
+        painter->restore();
+        return;
+    }
+
     auto *cv = qobject_cast<const ChatView *>(option.widget);
     bool singleTextSel = false;
     bool multiRowSel   = false;