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.h

@@ -14,6 +14,9 @@ enum MessageDataRole {
     MsgReactionsRole    = Qt::UserRole + 9,
     MsgIdRole           = Qt::UserRole + 10,
     MsgIsOutgoingRole   = Qt::UserRole + 11,
+    MsgContentTypeRole  = Qt::UserRole + 12,
+    MsgVoiceDurationRole = Qt::UserRole + 13,
+    MsgVoiceFileRole    = Qt::UserRole + 14,
     MsgAuthorNodeIdRole = Qt::UserRole + 20,
 };
 
@@ -46,6 +49,10 @@ private:
         int emojiCount = 0;
         QRect emojiArea;
         bool isOutgoing = false;
+        bool isVoice = false;
+        QRect voicePlayBtnRect;
+        QRect voiceDurationRect;
+        QString voiceDuration;
     };
 
     Layout calcLayout(const QStyleOptionViewItem &option,