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

frontend/admin/chat-log.html

@@ -0,0 +1,46 @@
+<div class="panel-header-row">
+    <div>
+        <h1>Chat Log</h1>
+        <p>Browse and manage stored chat messages.</p>
+    </div>
+    <div class="button-row">
+        <button id="reload-chat-log-btn" type="button" class="btn btn-secondary">Reload</button>
+        <button id="bulk-delete-chat-log-btn" type="button" class="btn btn-danger" disabled>Delete Selected</button>
+    </div>
+</div>
+
+<div class="panel-card">
+    <div class="chat-log-filters">
+        <input id="chat-log-filter-room" class="text-input" type="text" placeholder="Room" />
+        <input id="chat-log-filter-username" class="text-input" type="text" placeholder="Username" />
+        <input id="chat-log-filter-text" class="text-input" type="text" placeholder="Message text" />
+        <button id="chat-log-filter-btn" type="button" class="btn btn-secondary">Filter</button>
+        <button id="chat-log-clear-filter-btn" type="button" class="btn btn-secondary">Clear</button>
+    </div>
+</div>
+
+<div class="panel-card">
+    <div class="table-wrap">
+        <table class="data-table">
+            <thead>
+                <tr>
+                    <th><input type="checkbox" id="chat-log-select-all" title="Select all" /></th>
+                    <th>ID</th>
+                    <th>Room</th>
+                    <th>Username</th>
+                    <th>Message</th>
+                    <th>Type</th>
+                    <th>Timestamp</th>
+                    <th>Actions</th>
+                </tr>
+            </thead>
+            <tbody id="chat-log-table-body"></tbody>
+        </table>
+    </div>
+    <div class="chat-log-pagination">
+        <button id="chat-log-prev-btn" type="button" class="btn btn-secondary" disabled>Previous</button>
+        <span id="chat-log-page-info" class="small-muted">Page 1</span>
+        <button id="chat-log-next-btn" type="button" class="btn btn-secondary" disabled>Next</button>
+    </div>
+    <p id="chat-log-status" class="status-line" aria-live="polite">Loading chat log...</p>
+</div>