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/S46wifi

@@ -0,0 +1,44 @@
+#!/bin/sh
+# S46wifi — ansluter till WiFi via wpa_supplicant
+#
+# Körs efter S45wifi-bt (GPIO aktivering av chipet).
+# Använder /etc/wpa_supplicant.conf för nätverkslista.
+
+IFACE="wlan0"
+PIDFILE="/var/run/wpa_supplicant.pid"
+LOG="/var/log/wifi.log"
+
+case "$1" in
+    start)
+        echo "Starting WiFi"
+        ip link set "$IFACE" up
+        sleep 2
+
+        wpa_supplicant -B \
+            -i "$IFACE" \
+            -c /etc/wpa_supplicant.conf \
+            -P "$PIDFILE" \
+            >> "$LOG" 2>&1
+
+        # Hämta IP via DHCP
+        sleep 3
+        dhclient "$IFACE" >> "$LOG" 2>&1 || \
+        udhcpc -i "$IFACE" -b -p /var/run/udhcpc.pid >> "$LOG" 2>&1
+
+        echo "OK"
+        ;;
+    stop)
+        echo "Stopping WiFi"
+        [ -f "$PIDFILE" ] && kill $(cat "$PIDFILE") 2>/dev/null
+        rm -f "$PIDFILE"
+        ip link set "$IFACE" down
+        echo "OK"
+        ;;
+    restart)
+        $0 stop; sleep 1; $0 start
+        ;;
+    *)
+        echo "Usage: $0 {start|stop|restart}" >&2
+        exit 1
+        ;;
+esac