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

@@ -0,0 +1,27 @@
+# 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"