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

tests/unit/test_websocket_service.py

@@ -433,6 +433,63 @@ class TestWebSocketService:
         assert call_args["data"]["code"] == error_code
         assert call_args["data"]["message"] == error_message
 
+    @pytest.mark.asyncio
+    async def test_broadcast_scan_started(self, service, mock_websocket):
+        """Test broadcasting scan started event."""
+        connection_id = "test-conn"
+        directory = "/home/user/anime"
+
+        await service.connect(mock_websocket, connection_id)
+        await service.broadcast_scan_started(directory)
+
+        assert mock_websocket.send_json.called
+        call_args = mock_websocket.send_json.call_args[0][0]
+        assert call_args["type"] == "scan_started"
+        assert call_args["data"]["directory"] == directory
+        assert "timestamp" in call_args
+
+    @pytest.mark.asyncio
+    async def test_broadcast_scan_progress(self, service, mock_websocket):
+        """Test broadcasting scan progress event."""
+        connection_id = "test-conn"
+        directories_scanned = 25
+        files_found = 150
+        current_directory = "/home/user/anime/Attack on Titan"
+
+        await service.connect(mock_websocket, connection_id)
+        await service.broadcast_scan_progress(
+            directories_scanned, files_found, current_directory
+        )
+
+        assert mock_websocket.send_json.called
+        call_args = mock_websocket.send_json.call_args[0][0]
+        assert call_args["type"] == "scan_progress"
+        assert call_args["data"]["directories_scanned"] == directories_scanned
+        assert call_args["data"]["files_found"] == files_found
+        assert call_args["data"]["current_directory"] == current_directory
+        assert "timestamp" in call_args
+
+    @pytest.mark.asyncio
+    async def test_broadcast_scan_completed(self, service, mock_websocket):
+        """Test broadcasting scan completed event."""
+        connection_id = "test-conn"
+        total_directories = 100
+        total_files = 500
+        elapsed_seconds = 12.5
+
+        await service.connect(mock_websocket, connection_id)
+        await service.broadcast_scan_completed(
+            total_directories, total_files, elapsed_seconds
+        )
+
+        assert mock_websocket.send_json.called
+        call_args = mock_websocket.send_json.call_args[0][0]
+        assert call_args["type"] == "scan_completed"
+        assert call_args["data"]["total_directories"] == total_directories
+        assert call_args["data"]["total_files"] == total_files
+        assert call_args["data"]["elapsed_seconds"] == elapsed_seconds
+        assert "timestamp" in call_args
+
 
 class TestGetWebSocketService:
     """Test cases for get_websocket_service factory function."""