feat: audio stack working — pulseaudio + x6200_control + voice_rec

- Add pulseaudio in system mode
- Add alsactl restore with correct mixer state from Aether
- Add x6200-control package (I2C hardware control library)
- Audio chain: pulseaudio -> x6200_control_init -> voice_rec -> speaker

br2_external/board/x6200/rootfs-overlay/etc/init.d/S70mestre-audio

@@ -0,0 +1,59 @@
+#!/bin/sh
+# S70mestre-audio — X6200 audio hardware init
+#
+# Initializes the X6200's audio routing via I2C:
+#   1. Calls x6200_control_init() to establish MCU state
+#   2. Sets speaker volume
+#   3. Switches audio routing from RX-radio to SoC DAC (voice_rec)
+#
+# Must run after S50pulseaudio (pulseaudio must hold PCM open first
+# to keep ALSA clocks active).
+#
+# The voice_rec bit (0x00008 in sple_atue_trx register, cmd 12)
+# switches the X6200's internal audio mux from the RF receiver
+# to the SoC DAC — allowing piHPSDR/aplay to be heard in the speaker.
+
+VOLUME=50
+
+do_init() {
+    python3 << EOF
+import ctypes
+lib = ctypes.CDLL("libaether_x6200_control.so")
+lib.x6200_control_init.restype = ctypes.c_bool
+lib.x6200_control_rxvol_set.argtypes = [ctypes.c_uint8]
+lib.x6200_control_spmode_set.argtypes = [ctypes.c_bool]
+
+if not lib.x6200_control_init():
+    raise SystemExit("x6200_control_init() failed")
+
+lib.x6200_control_rxvol_set($VOLUME)
+lib.x6200_control_spmode_set(False)  # Speaker mode (not headphone)
+EOF
+}
+
+do_voice_rec() {
+    # Switch audio routing: RX-radio -> SoC DAC (voice_rec bit = 0x00008)
+    i2ctransfer -y 0 w6@0x72 0x00 0x30 0x08 0x00 0x00 0x00
+}
+
+case "$1" in
+    start)
+        echo "Starting mestre-audio"
+        do_init && do_voice_rec && echo "OK" || echo "FAILED"
+        ;;
+    stop)
+        echo "Stopping mestre-audio"
+        # Switch back to RX-radio audio
+        i2ctransfer -y 0 w6@0x72 0x00 0x30 0x00 0x00 0x00 0x00
+        echo "OK"
+        ;;
+    restart)
+        $0 stop
+        sleep 1
+        $0 start
+        ;;
+    *)
+        echo "Usage: $0 {start|stop|restart}" >&2
+        exit 1
+        ;;
+esac