Add MP4 scan progress visibility in UI

- Add broadcast_scan_started, broadcast_scan_progress, broadcast_scan_completed to WebSocketService
- Inject WebSocketService into AnimeService for real-time scan progress broadcasts
- Add CSS styles for scan progress overlay with spinner, stats, and completion state
- Update app.js to handle scan events and display progress overlay
- Add unit tests for new WebSocket broadcast methods
- All 1022 tests passing

src/server/web/static/css/styles.css

@@ -1898,4 +1898,190 @@ body {
 .backup-actions .btn {
   padding: 4px 8px;
   font-size: 0.8em;
+}
+
+/* ========================================
+   Scan Progress Overlay Styles
+   ======================================== */
+
+.scan-progress-overlay {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  background-color: rgba(0, 0, 0, 0.6);
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  z-index: 3000;
+  opacity: 0;
+  visibility: hidden;
+  transition: opacity 0.3s ease, visibility 0.3s ease;
+}
+
+.scan-progress-overlay.visible {
+  opacity: 1;
+  visibility: visible;
+}
+
+.scan-progress-container {
+  background-color: var(--color-surface);
+  border: 1px solid var(--color-border);
+  border-radius: var(--border-radius-lg);
+  box-shadow: var(--shadow-elevated);
+  padding: var(--spacing-xxl);
+  max-width: 450px;
+  width: 90%;
+  text-align: center;
+  animation: scanProgressSlideIn 0.3s ease;
+}
+
+@keyframes scanProgressSlideIn {
+  from {
+    transform: translateY(-20px);
+    opacity: 0;
+  }
+  to {
+    transform: translateY(0);
+    opacity: 1;
+  }
+}
+
+.scan-progress-header {
+  margin-bottom: var(--spacing-lg);
+}
+
+.scan-progress-header h3 {
+  margin: 0;
+  font-size: var(--font-size-title);
+  color: var(--color-text-primary);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--spacing-sm);
+}
+
+.scan-progress-spinner {
+  display: inline-block;
+  width: 24px;
+  height: 24px;
+  border: 3px solid var(--color-bg-tertiary);
+  border-top-color: var(--color-accent);
+  border-radius: 50%;
+  animation: scanSpinner 1s linear infinite;
+}
+
+@keyframes scanSpinner {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+.scan-progress-stats {
+  display: flex;
+  justify-content: space-around;
+  margin: var(--spacing-lg) 0;
+  padding: var(--spacing-md) 0;
+  border-top: 1px solid var(--color-border);
+  border-bottom: 1px solid var(--color-border);
+}
+
+.scan-stat {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: var(--spacing-xs);
+}
+
+.scan-stat-value {
+  font-size: var(--font-size-large-title);
+  font-weight: 600;
+  color: var(--color-accent);
+  line-height: 1;
+}
+
+.scan-stat-label {
+  font-size: var(--font-size-caption);
+  color: var(--color-text-secondary);
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.scan-current-directory {
+  margin-top: var(--spacing-md);
+  padding: var(--spacing-sm) var(--spacing-md);
+  background-color: var(--color-bg-secondary);
+  border-radius: var(--border-radius-md);
+  font-size: var(--font-size-caption);
+  color: var(--color-text-secondary);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  max-width: 100%;
+}
+
+.scan-current-directory-label {
+  font-weight: 500;
+  color: var(--color-text-tertiary);
+  margin-right: var(--spacing-xs);
+}
+
+/* Scan completed state */
+.scan-progress-container.completed .scan-progress-spinner {
+  display: none;
+}
+
+.scan-progress-container.completed .scan-progress-header h3 {
+  color: var(--color-success);
+}
+
+.scan-completed-icon {
+  display: none;
+  width: 24px;
+  height: 24px;
+  color: var(--color-success);
+}
+
+.scan-progress-container.completed .scan-completed-icon {
+  display: inline-block;
+}
+
+.scan-progress-container.completed .scan-stat-value {
+  color: var(--color-success);
+}
+
+.scan-elapsed-time {
+  margin-top: var(--spacing-md);
+  font-size: var(--font-size-body);
+  color: var(--color-text-secondary);
+}
+
+.scan-elapsed-time i {
+  margin-right: var(--spacing-xs);
+  color: var(--color-text-tertiary);
+}
+
+/* Responsive adjustments for scan overlay */
+@media (max-width: 768px) {
+  .scan-progress-container {
+    padding: var(--spacing-lg);
+    max-width: 95%;
+  }
+
+  .scan-progress-stats {
+    flex-direction: column;
+    gap: var(--spacing-md);
+  }
+
+  .scan-stat {
+    flex-direction: row;
+    justify-content: space-between;
+    width: 100%;
+    padding: 0 var(--spacing-md);
+  }
+
+  .scan-stat-value {
+    font-size: var(--font-size-title);
+  }
 }