feat: implement MoveCommand for undoable layer movement

Critical Fix - Move Tool Undo/Redo:
- Create MoveCommand class to track layer position changes
- Capture initial and final positions during move operation
- Only add to history if position actually changed
- Real-time visual feedback during drag (via updateLayer)
- Single undo point per move operation (not per pixel)

Command Pattern:
- MoveCommand extends BaseCommand
- Implements execute() and undo() methods
- captureAfterPosition() called on pointer up
- hasChanged() prevents no-op entries in history

Files:
- core/commands/move-command.ts - New command class
- tools/move-tool.ts - Updated to use MoveCommand
- core/commands/index.ts - Export MoveCommand

This fixes the critical issue where moving layers had no undo support.
Users can now undo/redo layer movements as expected.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

core/commands/index.ts

@@ -1,3 +1,4 @@
 export * from './base-command';
 export * from './layer-commands';
 export * from './draw-command';
+export * from './move-command';

core/commands/move-command.ts

@@ -0,0 +1,60 @@
+import { BaseCommand } from './base-command';
+import { useLayerStore } from '@/store/layer-store';
+
+/**
+ * Command for moving a layer
+ * Captures start and end positions for undo/redo
+ */
+export class MoveCommand extends BaseCommand {
+  private layerId: string;
+  private beforePosition: { x: number; y: number };
+  private afterPosition: { x: number; y: number } | null = null;
+
+  constructor(layerId: string, beforePosition: { x: number; y: number }) {
+    super('Move Layer');
+    this.layerId = layerId;
+    this.beforePosition = beforePosition;
+  }
+
+  /**
+   * Capture the final position after the move is complete
+   */
+  captureAfterPosition(x: number, y: number): void {
+    this.afterPosition = { x, y };
+  }
+
+  execute(): void {
+    if (!this.afterPosition) {
+      // No-op on first execute (position already set during drag)
+      return;
+    }
+
+    // Restore after position (for redo)
+    const { updateLayer } = useLayerStore.getState();
+    updateLayer(this.layerId, {
+      x: this.afterPosition.x,
+      y: this.afterPosition.y,
+      updatedAt: Date.now(),
+    });
+  }
+
+  undo(): void {
+    const { updateLayer } = useLayerStore.getState();
+    updateLayer(this.layerId, {
+      x: this.beforePosition.x,
+      y: this.beforePosition.y,
+      updatedAt: Date.now(),
+    });
+  }
+
+  /**
+   * Check if this move actually changed position
+   */
+  hasChanged(): boolean {
+    if (!this.afterPosition) return false;
+    return (
+      this.beforePosition.x !== this.afterPosition.x ||
+      this.beforePosition.y !== this.afterPosition.y
+    );
+  }
+}