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/package/x6200-control/x6200-control.mk

@@ -0,0 +1,24 @@
+################################################################################
+#
+# x6200-control
+#
+# Aether-Radio's base control library for the Xiegu X6200. Provides
+# I2C-based control of the radio's MCU/FPGA: audio routing, VFO, mode,
+# AGC, ATU, TX/RX state, etc.
+#
+################################################################################
+
+X6200_CONTROL_VERSION = v0.1.0
+X6200_CONTROL_SITE = https://github.com/gdyuldin/X6200Control
+X6200_CONTROL_SITE_METHOD = git
+X6200_CONTROL_LICENSE = LGPL-2.1-or-later
+X6200_CONTROL_LICENSE_FILES = LICENSE
+X6200_CONTROL_INSTALL_STAGING = YES
+X6200_CONTROL_DEPENDENCIES = libgpiod
+
+# Disable LTO; keeps the build simple and avoids cross-toolchain issues.
+X6200_CONTROL_CONF_OPTS = \
+	-DAETHER_X6200CTRL_USE_LTO=OFF \
+	-DBUILD_SHARED_LIBS=ON
+
+$(eval $(cmake-package))