Add web GUI, docs, scripts, and 5G router config

- Web app (Flask): status, config, firewall, logs, users, restart
- Docs: AT commands, deploy, DNS, quickstart, web GUI
- Scripts: connect, deploy, diag, healthcheck, modem-status, speedtest, status, troubleshoot
- Init and iptables: 5g-router, 5g-webgui, rules.v4
- CHANGELOG, TODO, REVISION; config and README updates

scripts/healthcheck-5g.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+# Alpine 5G Router – health check for monitoring (Nagios, Uptime Kuma, etc.)
+# Exit 0 = OK, 1 = 5G down or no connectivity
+# Usage: healthcheck-5g.sh [--ping-only]
+# Rev: 1  (see REVISION in repo root)
+
+CONFIG="/etc/5g-router.conf"
+WAN_IF="${WAN_IF:-eth1}"
+[ -f "$CONFIG" ] && . "$CONFIG"
+
+PING_TARGET="${PING_TARGET:-8.8.8.8}"
+
+# Check default route goes via 5G
+def_if=$(ip route show default 2>/dev/null | awk '{print $5}' | head -1)
+if [ "$def_if" != "$WAN_IF" ]; then
+    echo "CRITICAL: default route not via $WAN_IF (got: $def_if)"
+    exit 1
+fi
+
+# Check WAN has an address
+wan_ip=$(ip -4 addr show "$WAN_IF" 2>/dev/null | grep -oE 'inet [0-9.]+' | awk '{print $2}')
+if [ -z "$wan_ip" ]; then
+    echo "CRITICAL: no IP on $WAN_IF"
+    exit 1
+fi
+
+if [ "$1" = "--ping-only" ]; then
+    if ping -c 1 -W 3 "$PING_TARGET" >/dev/null 2>&1; then
+        echo "OK: ping $PING_TARGET"
+        exit 0
+    else
+        echo "CRITICAL: ping $PING_TARGET failed"
+        exit 1
+    fi
+fi
+
+# Full check: route + ping
+if ping -c 2 -W 5 "$PING_TARGET" >/dev/null 2>&1; then
+    echo "OK: 5G up, ping $PING_TARGET"
+    exit 0
+else
+    echo "CRITICAL: 5G route OK but ping $PING_TARGET failed"
+    exit 1
+fi