feat: implement Phase 5 - Advanced Color System

Complete color management system with picker, swatches, and eyedropper:

**Color Utilities (lib/color-utils.ts)**
- RGB ↔ Hex conversion
- RGB ↔ HSV conversion
- Color validation (isValidHex)
- getColorAtPoint for eyedropper
- Default 20-color palette
- Hex normalization

**Color Store (store/color-store.ts)**
- Primary/secondary color management
- Recent colors history (max 20)
- Custom swatches (max 20)
- Color swap functionality
- Zustand persist middleware (localStorage)

**Components**

ColorPicker:
- HSV color space selector
- Interactive saturation/value picker (200x160px)
- Hue slider (vertical gradient)
- Hex input with validation
- RGB value display
- Pointer drag support
- Real-time updates
- Color preview

ColorSwatches:
- Default 20-color palette grid (10x2)
- Custom swatches with add/remove
- Active color highlighting
- Hover scaling effect
- Delete button on hover
- Color tooltips

ColorPanel:
- Tabbed interface (Picker/Swatches/Recent)
- Primary/Secondary color display
- Color swap button
- Recent colors grid (max 20)
- Tab navigation (Palette/Clock icons)
- 256px wide panel
- Persistent state

**Eyedropper Tool**
- Pick color from active layer
- Click or drag to sample
- Updates primary color
- Integrates with ColorPanel
- Crosshair cursor

**Features**
✓ HSV color picker with gradient
✓ Hex color input validation
✓ RGB value display
✓ 20 default color swatches
✓ Unlimited custom swatches (max 20 stored)
✓ Recent colors auto-tracking
✓ Primary/secondary color swap
✓ Eyedropper tool to sample canvas
✓ Persistent color preferences
✓ Smooth drag interactions
✓ Real-time color updates

**Integration**
- EditorLayout: Added ColorPanel (256px)
- ToolPalette: Added Eyedropper icon
- CanvasWithTools: Eyedropper support
- Tool settings: Removed basic color picker
- Color syncs with tool store

**UI/UX**
- 3-tab navigation (Picker, Swatches, Recent)
- Primary color: Large square
- Secondary color: Small overlap square
- Active tab highlighting
- Hover effects on all swatches
- Smooth transitions
- Keyboard accessible

**Performance**
- Efficient HSV calculations
- LocalStorage persistence
- Pointer event optimization
- Drag state management
- Build time: ~1.3s

**State Management**
- Zustand store with persist
- Auto-add to recent on use
- Max limits prevent memory bloat
- Clean swap operation

Ready for Phase 6: File Operations

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

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

store/index.ts

@@ -2,3 +2,4 @@ export * from './canvas-store';
 export * from './layer-store';
 export * from './tool-store';
 export * from './history-store';
+export * from './color-store';