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

etc/init.d/5g-router

@@ -0,0 +1,45 @@
+#!/sbin/openrc-run
+# Alpine 5G Router – OpenRC service
+# Start: run connect-5g.sh. Stop: bring down WAN interface (optional).
+# Rev: 5  (see REVISION in repo root)
+
+description="5G modem connection (connect-5g.sh)"
+command="/usr/local/bin/connect-5g.sh"
+command_background="yes"
+output_log="/var/log/5g-router.log"
+error_log="/var/log/5g-router.log"
+pidfile="/run/5g-router.pid"
+# connect-5g.sh runs run_once then sleep infinity so the process stays up; stop with service 5g-router stop
+
+# Load config for WAN_IF if we need to clean up on stop
+[ -f /etc/5g-router.conf ] && . /etc/5g-router.conf
+WAN_IF="${WAN_IF:-eth1}"
+
+depend() {
+    need net
+    after bootmisc
+}
+
+# Idempotent start: if already running, succeed instead of "already running" error
+start() {
+    if [ -f "$pidfile" ] && kill -0 "$(cat "$pidfile")" 2>/dev/null; then
+        ebegin "Starting 5g-router"
+        eend 0 "Already running"
+        return 0
+    fi
+    ebegin "Starting 5g-router"
+    start-stop-daemon --start --background --pidfile "$pidfile" --make-pidfile \
+        --stdout "$output_log" --stderr "$error_log" \
+        --exec "$command"
+    eend $?
+}
+
+start_pre() {
+    return 0
+}
+
+stop_post() {
+    # Optionally bring down 5G interface so traffic uses other default route
+    ip link set "$WAN_IF" down 2>/dev/null || true
+    return 0
+}