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

.gitignore

@@ -14,3 +14,8 @@ Thumbs.db
 # Backup files
 *.bak
 *.backup
+
+# Web GUI – sensitive / generated
+web/data/users.json
+web/data/*.db
+web/data/*.db-journal