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/board/x6200/rootfs-overlay/etc/init.d/S85bt-keyboard

@@ -0,0 +1,58 @@
+#!/bin/sh
+# S85bt-keyboard — auto-connect Linocell BTK16 BT-tangentbord
+#
+# Försöker ansluta tangentbordet vid boot och startar en bakgrundsprocess
+# som reconnectar automatiskt när tangentbordet kommer inom räckhåll.
+#
+# Tangentbordet måste vara parat och trustat sedan tidigare.
+# Para manuellt med: bluetoothctl pair ED:96:00:23:E2:02
+#                    bluetoothctl trust ED:96:00:23:E2:02
+
+KEYBOARD_ADDR="ED:96:00:23:E2:02"
+PIDFILE="/var/run/bt-keyboard.pid"
+LOG="/var/log/bt-keyboard.log"
+
+connect_keyboard() {
+    bluetoothctl power on > /dev/null 2>&1
+    bluetoothctl connect "$KEYBOARD_ADDR" > /dev/null 2>&1
+}
+
+watch_loop() {
+    while true; do
+        # Kolla om tangentbordet är anslutet
+        if ! bluetoothctl info "$KEYBOARD_ADDR" 2>/dev/null | grep -q "Connected: yes"; then
+            connect_keyboard
+        fi
+        sleep 10
+    done
+}
+
+case "$1" in
+    start)
+        echo "Starting BT keyboard auto-connect"
+
+        # Försök första anslutning i bakgrunden (tangentbordet kanske inte är i närheten)
+        (sleep 5 && connect_keyboard) &
+
+        # Starta watch-loop som reconnectar när tgb dyker upp
+        watch_loop >> "$LOG" 2>&1 &
+        echo $! > "$PIDFILE"
+        echo "OK"
+        ;;
+    stop)
+        echo "Stopping BT keyboard auto-connect"
+        if [ -f "$PIDFILE" ]; then
+            kill $(cat "$PIDFILE") 2>/dev/null
+            rm -f "$PIDFILE"
+        fi
+        bluetoothctl disconnect "$KEYBOARD_ADDR" > /dev/null 2>&1
+        echo "OK"
+        ;;
+    restart)
+        $0 stop; sleep 1; $0 start
+        ;;
+    *)
+        echo "Usage: $0 {start|stop|restart}" >&2
+        exit 1
+        ;;
+esac