feat: implement Phase 2 - Core Canvas Engine with layer system

Complete canvas rendering infrastructure and state management:

**Type System (types/)**
- Layer interface with blend modes, opacity, visibility
- Canvas state with zoom, pan, grid, rulers
- Tool types and settings interfaces
- Selection and pointer state types

**State Management (store/)**
- Layer store: CRUD operations, reordering, merging, flattening
- Canvas store: zoom (0.1x-10x), pan, grid, rulers, coordinate conversion
- Tool store: active tool, brush settings (size, opacity, hardness, flow)
- Full Zustand integration with selectors

**Utilities (lib/)**
- Canvas utils: create, clone, resize, load images, draw grid/checkerboard
- General utils: cn, clamp, lerp, distance, snap to grid, debounce, throttle
- Image data handling with error safety

**Components**
- CanvasWrapper: Multi-layer rendering with transformations
  - Checkerboard transparency background
  - Layer compositing with blend modes and opacity
  - Grid overlay support
  - Selection visualization
  - Mouse wheel zoom (Ctrl+scroll)
  - Middle-click or Shift+click panning

- LayersPanel: Interactive layer management
  - Visibility toggle with eye icon
  - Active layer selection
  - Opacity display
  - Delete with confirmation
  - Sorted by z-order

- EditorLayout: Full editor interface
  - Top toolbar with zoom controls (±, fit to screen, percentage)
  - Canvas area with full viewport
  - Right sidebar for layers panel
  - "New Layer" button with auto-naming

**Features Implemented**
✓ Multi-layer canvas with proper z-ordering
✓ Layer visibility, opacity, blend modes
✓ Zoom: 10%-1000% with Ctrl+wheel
✓ Pan: Middle-click or Shift+drag
✓ Grid overlay (toggleable)
✓ Selection rendering
✓ Background color support
✓ Create/delete/duplicate layers
✓ Layer merging and flattening

**Performance**
- Dev server: 451ms startup
- Efficient canvas rendering with transformations
- Debounced/throttled event handlers ready
- Memory-safe image data operations

Ready for Phase 3: History & Undo System

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

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

store/tool-store.ts

@@ -0,0 +1,107 @@
+import { create } from 'zustand';
+import type { ToolType, ToolSettings, ToolState } from '@/types';
+
+interface ToolStore extends ToolState {
+  /** Set active tool */
+  setActiveTool: (tool: ToolType) => void;
+  /** Update tool settings */
+  updateSettings: (settings: Partial<ToolSettings>) => void;
+  /** Set brush size */
+  setSize: (size: number) => void;
+  /** Set opacity */
+  setOpacity: (opacity: number) => void;
+  /** Set hardness */
+  setHardness: (hardness: number) => void;
+  /** Set color */
+  setColor: (color: string) => void;
+  /** Set flow */
+  setFlow: (flow: number) => void;
+  /** Set spacing */
+  setSpacing: (spacing: number) => void;
+  /** Reset settings to defaults */
+  resetSettings: () => void;
+}
+
+const DEFAULT_SETTINGS: ToolSettings = {
+  size: 10,
+  opacity: 1,
+  hardness: 1,
+  color: '#000000',
+  flow: 1,
+  spacing: 0.25,
+};
+
+export const useToolStore = create<ToolStore>((set) => ({
+  activeTool: 'brush',
+  settings: { ...DEFAULT_SETTINGS },
+  cursor: 'crosshair',
+
+  setActiveTool: (tool) => {
+    const cursors: Record<ToolType, string> = {
+      select: 'crosshair',
+      move: 'move',
+      pencil: 'crosshair',
+      brush: 'crosshair',
+      eraser: 'crosshair',
+      fill: 'crosshair',
+      eyedropper: 'crosshair',
+      text: 'text',
+      shape: 'crosshair',
+      crop: 'crosshair',
+      clone: 'crosshair',
+      blur: 'crosshair',
+      sharpen: 'crosshair',
+    };
+
+    set({
+      activeTool: tool,
+      cursor: cursors[tool],
+    });
+  },
+
+  updateSettings: (settings) => {
+    set((state) => ({
+      settings: { ...state.settings, ...settings },
+    }));
+  },
+
+  setSize: (size) => {
+    set((state) => ({
+      settings: { ...state.settings, size: Math.max(1, Math.min(1000, size)) },
+    }));
+  },
+
+  setOpacity: (opacity) => {
+    set((state) => ({
+      settings: { ...state.settings, opacity: Math.max(0, Math.min(1, opacity)) },
+    }));
+  },
+
+  setHardness: (hardness) => {
+    set((state) => ({
+      settings: { ...state.settings, hardness: Math.max(0, Math.min(1, hardness)) },
+    }));
+  },
+
+  setColor: (color) => {
+    set((state) => ({
+      settings: { ...state.settings, color },
+    }));
+  },
+
+  setFlow: (flow) => {
+    set((state) => ({
+      settings: { ...state.settings, flow: Math.max(0, Math.min(1, flow)) },
+    }));
+  },
+
+  setSpacing: (spacing) => {
+    set((state) => ({
+      settings: { ...state.settings, spacing: Math.max(0.01, Math.min(10, spacing)) },
+    }));
+  },
+
+  resetSettings: () => {
+    set({ settings: { ...DEFAULT_SETTINGS } });
+  },
+}));