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

web/templates/users.html

@@ -0,0 +1,17 @@
+{% extends "base.html" %}
+{% block title %}Users – Alpine 5G Router{% endblock %}
+{% block content %}
+<h2>Users (admin only)</h2>
+<div class="table-wrap">
+  <table>
+    <thead>
+      <tr><th>Username</th><th>Role</th><th>Actions</th></tr>
+    </thead>
+    <tbody id="usersTable"></tbody>
+  </table>
+</div>
+<div class="actions" style="margin-top: 1rem;">
+  <button type="button" class="btn btn-primary" id="addUserBtn">Add user</button>
+</div>
+<div id="usersMsg" class="msg"></div>
+{% endblock %}