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/5g-router.conf.example

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+# Alpine 5G Router – configuration example
+# Copy to /etc/5g-router.conf and edit. Used by connect-5g.sh and configure_fm350_5g.sh
+
+# Modem
+AT_PORT="/dev/ttyUSB1"
+APN="internet"
+
+# Interfaces (WAN = 5G modem RNDIS, LAN = VLAN for clients)
+WAN_IF="eth1"
+LAN_IF="eth0.100"
+
+# Optional: fallback to eth0 when 5G is down (use ethernet as default route)
+FAILOVER_ENABLED="no"
+FAILOVER_IF="eth0"
+FAILOVER_METRIC="202"
+
+# Watchdog: re-check 5G connectivity every N seconds (0 = disabled, run once)
+WATCHDOG_INTERVAL="0"
+
+# Log signal strength to /var/log/5g-router.log (yes/no)
+LOG_SIGNAL="yes"
+
+# Alert when signal CSQ below this (0 = disabled)
+WEAK_SIGNAL_CSQ="10"
+
+# Optional: DNS servers (used when 5G is up; comma-separated)
+# DNS_SERVERS="195.14.130.220,195.14.154.100"

etc/init.d/5g-router

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+#!/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
+}

etc/init.d/5g-webgui

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+#!/sbin/openrc-run
+# Alpine 5G Router – Web GUI (Flask). Login: admin/support with different permissions.
+# Rev: 1  (see REVISION in repo root)
+
+description="5G Router Web GUI (port 5000)"
+command="/usr/local/share/5g-webgui/run.sh"
+command_background="yes"
+pidfile="/run/5g-webgui.pid"
+output_log="/var/log/5g-webgui.log"
+error_log="/var/log/5g-webgui.log"
+
+depend() {
+    need net
+    after bootmisc
+}
+
+start_pre() {
+    if [ ! -f /usr/local/share/5g-webgui/app.py ]; then
+        eend 1 "Web GUI not installed at /usr/local/share/5g-webgui"
+        return 1
+    fi
+    if ! command -v python3 >/dev/null 2>&1; then
+        eend 1 "python3 not found. Install: apk add python3 py3-flask"
+        return 1
+    fi
+    return 0
+}

etc/iptables/rules.v4

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+# Alpine 5G Router – iptables rules (IPv4)
+# Restored at boot by iptables-restore service. Generated/updated by connect-5g.sh or install.
+# Ensure 5G WAN interface is eth1 and LAN is eth0.100; adjust if different.
+
+*filter
+:INPUT ACCEPT [0:0]
+:FORWARD ACCEPT [0:0]
+:OUTPUT ACCEPT [0:0]
+# Allow web GUI (port 5000) from eth0 (management access)
+-A INPUT -i eth0 -p tcp --dport 5000 -j ACCEPT
+# Allow LAN -> WAN (5G)
+-A FORWARD -i eth0.100 -o eth1 -j ACCEPT
+# Allow established/related WAN -> LAN
+-A FORWARD -i eth1 -o eth0.100 -m state --state RELATED,ESTABLISHED -j ACCEPT
+COMMIT
+
+*nat
+:PREROUTING ACCEPT [0:0]
+:INPUT ACCEPT [0:0]
+:OUTPUT ACCEPT [0:0]
+:POSTROUTING ACCEPT [0:0]
+# NAT LAN traffic going out 5G
+-A POSTROUTING -o eth1 -j MASQUERADE
+COMMIT