Add video viewer modal for gallery videos

- Click on video thumbnail to open in large viewer
- Video plays on hover, pauses when mouse leaves
- Close viewer by clicking X or clicking outside video

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/public/css/style.css

@@ -695,6 +695,52 @@ body {
     }
 }
 
+/* Video Viewer */
+.video-viewer {
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: rgba(0, 0, 0, 0.9);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 2000;
+}
+
+.video-viewer-close {
+    position: absolute;
+    top: 20px;
+    right: 20px;
+    width: 40px;
+    height: 40px;
+    border: none;
+    border-radius: 50%;
+    background: rgba(255, 255, 255, 0.2);
+    color: white;
+    font-size: 24px;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    transition: background 0.2s;
+}
+
+.video-viewer-close:hover {
+    background: rgba(255, 255, 255, 0.3);
+}
+
+.video-viewer-player {
+    max-width: 90vw;
+    max-height: 90vh;
+    border-radius: var(--radius);
+}
+
+.gallery-item-media video {
+    cursor: pointer;
+}
+
 /* Privacy Mode */
 .privacy-toggle.active {
     background: var(--primary);