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>

tools/move-tool.ts

@@ -1,12 +1,15 @@
 import { BaseTool } from './base-tool';
 import type { PointerState } from '@/types';
 import { useLayerStore } from '@/store/layer-store';
+import { useHistoryStore } from '@/store/history-store';
+import { MoveCommand } from '@/core/commands';
 
 export class MoveTool extends BaseTool {
   private startX = 0;
   private startY = 0;
   private layerStartX = 0;
   private layerStartY = 0;
+  private moveCommand: MoveCommand | null = null;
 
   constructor() {
     super('Move');
@@ -23,6 +26,9 @@ export class MoveTool extends BaseTool {
     this.startY = pointer.y;
     this.layerStartX = layer.x;
     this.layerStartY = layer.y;
+
+    // Create move command with initial position
+    this.moveCommand = new MoveCommand(layer.id, { x: layer.x, y: layer.y });
   }
 
   onPointerMove(pointer: PointerState): void {
@@ -34,6 +40,7 @@ export class MoveTool extends BaseTool {
     const dx = pointer.x - this.startX;
     const dy = pointer.y - this.startY;
 
+    // Update position in real-time (for visual feedback)
     const { updateLayer } = useLayerStore.getState();
     updateLayer(layer.id, {
       x: this.layerStartX + dx,
@@ -42,6 +49,21 @@ export class MoveTool extends BaseTool {
   }
 
   onPointerUp(): void {
+    if (this.moveCommand) {
+      const layer = this.getActiveLayer();
+      if (layer) {
+        // Capture final position
+        this.moveCommand.captureAfterPosition(layer.x, layer.y);
+
+        // Only add to history if position actually changed
+        if (this.moveCommand.hasChanged()) {
+          const { executeCommand } = useHistoryStore.getState();
+          executeCommand(this.moveCommand);
+        }
+      }
+      this.moveCommand = null;
+    }
+
     this.isDrawing = false;
     this.isActive = false;
   }