dm: прямой обмен сообщениями (DM) + soundtouch + архитектура звонков

- src/dm/: dm_core/dm_crypto/dm_mailbox — прямой обмен сообщениями (DM)
- lib/soundtouch-master/: vendored SoundTouch (изменение темпа/высоты аудио)
- doc/dm_arch.md, doc/chat_call_arch.md: архитектура DM и звонков
- tests: test_dm.c, test_dm_e2e.c
- chat: рефакторинг chat_* модулей, member_sync, invite_build
- chatgui/chatgui-android: синхронизация с новым API чата
- lib/u_async, debug_config, utun_instance: сопутствующие изменения

tools/chatgui/transport/gui_bridge_impl.cpp

@@ -49,6 +49,7 @@ static gui_admin_key_received_fn     g_admin_key_received_cb   = nullptr;
 static gui_invite_link_ready_fn      g_invite_link_ready_cb    = nullptr;
 static gui_invite_candidates_fn      g_invite_candidates_cb    = nullptr;
 static struct UASYNC*        g_ua                 = nullptr;
+static struct UTUN_INSTANCE* g_inst               = nullptr;
 
 /* ── GuiBridgeReceiver implementation ── */
 
@@ -255,6 +256,14 @@ void gui_bridge_set_uasync(struct UASYNC* ua) {
     if (g_receiver) g_receiver->ua = ua;
 }
 
+void gui_bridge_set_inst(struct UTUN_INSTANCE* inst) {
+    g_inst = inst;
+}
+
+struct UTUN_INSTANCE* gui_bridge_get_inst(void) {
+    return g_inst;
+}
+
 void gui_bridge_post(int event_type, const uint8_t* data, int data_len) {
     if (!g_receiver) { DEBUG_WARN(DEBUG_CATEGORY_DEBUG, "gui_bridge_post: g_receiver=NULL, dropping event %d", event_type); return; }