feat: add chat log admin management and refactor admin panel to lazy-load tab content

frontend/admin/users.html

@@ -0,0 +1,23 @@
+<div class="panel-header-row">
+    <div>
+        <h1>Users</h1>
+        <p>Current room presence derived from Redis presence keys.</p>
+    </div>
+    <button id="reload-users-btn" type="button" class="btn btn-secondary">Reload users</button>
+</div>
+
+<div class="panel-card">
+    <div class="table-wrap">
+        <table class="data-table">
+            <thead>
+                <tr>
+                    <th>Username</th>
+                    <th>Room</th>
+                    <th>Online</th>
+                </tr>
+            </thead>
+            <tbody id="users-table-body"></tbody>
+        </table>
+    </div>
+    <p id="users-status" class="status-line" aria-live="polite">Loading active users...</p>
+</div>