feat(phase-13): implement crop tool with visual guides and handles

Add comprehensive crop tool with visual guides, resize handles, and Apply/Cancel UI.

Features:
- Interactive crop area selection with drag-to-create
- 8 resize handles (corners and edges) for precise cropping
- Visual overlay with dimmed areas outside crop region
- Rule of thirds grid overlay for composition guidance
- Drag crop area to reposition
- Apply/Cancel buttons in tool options
- White border and handles for clear visibility

Changes:
- Created tools/crop-tool.ts with CropTool class
- Added crop tool to lib/tool-loader.ts
- Added Crop icon and button to tool palette with 'C' shortcut
- Added crop tool options UI in components/editor/tool-options.tsx
- Exported CropTool from tools/index.ts

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

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

lib/tool-loader.ts

@@ -113,6 +113,11 @@ async function loadTool(toolKey: string): Promise<BaseTool> {
         tool = new DodgeBurnTool();
         break;
       }
+      case 'crop': {
+        const { CropTool } = await import('@/tools/crop-tool');
+        tool = new CropTool();
+        break;
+      }
       default: {
         // Fallback to pencil tool
         const { PencilTool } = await import('@/tools/pencil-tool');