feat: M3 complete — WiFi, BT keyboard and mouse

Bluetooth (RTL8723D USB combo chip):
- GPIO pin 357 (active low) enables WiFi/BT hardware via x6200_gpio_set()
- bluez5_utils 5.64 (downgraded from 5.79 — HID input plugin broken in 5.79)
- rtl8723d_config.bin added to overlay (missing from linux-firmware package)
- S45wifi-bt: GPIO enable + modprobe btusb/uhid/hidp at boot
- S85bt-keyboard: auto-connect loop with scan+connect every 20s

WiFi (RTL8723DU):
- out-of-tree lwfinger/rtw88 driver (RTW88_8723DU not in kernel 6.1 mainline)
- linux-firmware RTL_RTW88 for rtw88/rtw8723d_fw.bin
- regulatory.db for cfg80211
- wpa_supplicant with multi-network config in /etc/wpa_supplicant.conf
- S46wifi: wpa_supplicant + udhcpc at boot

Key findings:
- RTL8723D USB WiFi (0bda:d723) requires out-of-tree rtw88 on kernel 6.1
- BT and WiFi share same USB device, both need GPIO 357 = 0 to power on
- bluez5 5.79 HID input plugin not linked into bluetoothd (build system bug)

br2_external/package/rtw88/Config.in

@@ -0,0 +1,8 @@
+config BR2_PACKAGE_RTW88
+	bool "rtw88 out-of-tree WiFi driver"
+	depends on BR2_LINUX_KERNEL
+	help
+	  Out-of-tree Realtek rtw88 driver from lwfinger/rtw88.
+	  Adds RTL8723DU USB WiFi support not available in kernel 6.1.
+
+	  https://github.com/lwfinger/rtw88