feat: audio - add concurrent mixing, output switching, and device-aware UI

programs/include/montauk/syscall.h

@@ -514,6 +514,9 @@ namespace montauk {
     inline int audio_get_output(int handle) {
         return audio_ctl(handle, montauk::abi::AUDIO_CTL_GET_OUTPUT, 0);
     }
+    inline int audio_set_output(int output) {
+        return audio_ctl(-1, montauk::abi::AUDIO_CTL_SET_OUTPUT, output);
+    }
     inline int audio_bt_status(int handle) {
         return audio_ctl(handle, montauk::abi::AUDIO_CTL_BT_STATUS, 0);
     }