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

frontend/admin/playlist.html

@@ -0,0 +1,16 @@
+<div class="panel-header-row">
+    <div>
+        <h1>Playlist</h1>
+        <p>Edit the active concat playlist used by the playout service.</p>
+    </div>
+    <div class="button-row">
+        <button id="reload-playlist-btn" type="button" class="btn btn-secondary">Reload</button>
+        <button id="save-playlist-btn" type="button" class="btn btn-primary">Save playlist</button>
+    </div>
+</div>
+
+<div class="panel-card">
+    <label for="playlist-content" class="sr-only">Playlist content</label>
+    <textarea id="playlist-content" class="text-input text-area" spellcheck="false"></textarea>
+    <p id="playlist-status" class="status-line" aria-live="polite">Loading playlist...</p>
+</div>