add timeline pkg to flutter

packages/z-timeline/lib/src/widgets/ghost_overlay.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/material.dart';
+
+import '../constants.dart';
+import '../models/entry_drag_state.dart';
+import '../services/layout_coordinate_service.dart';
+import '../services/time_scale_service.dart';
+import '../state/timeline_viewport_notifier.dart';
+
+/// A semi-transparent ghost overlay showing where an entry will land.
+///
+/// Displayed during drag operations to give visual feedback about the
+/// target position.
+class GhostOverlay extends StatelessWidget {
+  const GhostOverlay({
+    required this.dragState,
+    required this.viewport,
+    required this.contentWidth,
+    required this.laneHeight,
+    super.key,
+  });
+
+  final EntryDragState dragState;
+  final TimelineViewportNotifier viewport;
+  final double contentWidth;
+  final double laneHeight;
+
+  @override
+  Widget build(BuildContext context) {
+    final startX = TimeScaleService.mapTimeToPosition(
+      dragState.targetStart,
+      viewport.start,
+      viewport.end,
+    );
+    final endX = TimeScaleService.mapTimeToPosition(
+      dragState.targetEnd,
+      viewport.start,
+      viewport.end,
+    );
+
+    // Use centralized coordinate service to ensure ghost matches pill layout
+    final left = LayoutCoordinateService.normalizedToWidgetX(
+      normalizedX: startX,
+      contentWidth: contentWidth,
+    );
+    final width = LayoutCoordinateService.calculateItemWidth(
+      normalizedWidth: endX - startX,
+      contentWidth: contentWidth,
+    );
+    final top = LayoutCoordinateService.laneToY(
+      lane: dragState.targetLane,
+      laneHeight: laneHeight,
+    );
+
+    final scheme = Theme.of(context).colorScheme;
+
+    return Positioned(
+      left: left.clamp(0.0, double.infinity),
+      width: width.clamp(0.0, double.infinity),
+      top: top,
+      height: laneHeight,
+      child: IgnorePointer(
+        child: Container(
+          decoration: BoxDecoration(
+            color: scheme.primary.withValues(alpha: 0.3),
+            borderRadius: BorderRadius.circular(
+              ZTimelineConstants.pillBorderRadius,
+            ),
+            border: Border.all(
+              color: scheme.primary.withValues(alpha: 0.6),
+              width: 2,
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}