feat: implement resumable chunked media upload with progress indicators in admin UI

frontend/admin/index.html

@@ -64,9 +64,14 @@
                     <button id="reload-media-btn" type="button" class="btn btn-secondary">Reload library</button>
                 </div>
 
-                <div class="upload-dropzone">
+                <div id="upload-dropzone" class="upload-dropzone">
                     <input type="file" id="video-upload" accept="video/*,.mp4,.mov,.mkv,.webm" hidden />
                     <button id="upload-trigger-btn" type="button" class="btn btn-primary btn-large">Drag and Drop or Click to Upload</button>
+                    <p class="small-muted">Resumable chunk upload enabled • up to 2GB per file.</p>
+                    <div id="media-upload-progress-wrap" class="upload-progress" hidden>
+                        <progress id="media-upload-progress" value="0" max="100"></progress>
+                        <p id="media-upload-progress-text" class="small-muted">Uploading (0%)</p>
+                    </div>
                     <p id="media-status" class="status-line" aria-live="polite">Loading media library...</p>
                 </div>