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>

components/canvas/canvas-with-tools.tsx

@@ -10,6 +10,7 @@ import {
   BrushTool,
   EraserTool,
   FillTool,
+  EyedropperTool,
   type BaseTool,
 } from '@/tools';
 import type { PointerState } from '@/types';
@@ -21,6 +22,7 @@ const tools: Record<string, BaseTool> = {
   brush: new BrushTool(),
   eraser: new EraserTool(),
   fill: new FillTool(),
+  eyedropper: new EyedropperTool(),
 };
 
 export function CanvasWithTools() {
@@ -155,7 +157,7 @@ export function CanvasWithTools() {
     }
 
     // Drawing tools
-    if (e.button === 0 && !e.shiftKey && ['pencil', 'brush', 'eraser', 'fill'].includes(activeTool)) {
+    if (e.button === 0 && !e.shiftKey && ['pencil', 'brush', 'eraser', 'fill', 'eyedropper'].includes(activeTool)) {
       const activeLayer = getActiveLayer();
       if (!activeLayer || !activeLayer.canvas || activeLayer.locked) return;
 
@@ -198,7 +200,7 @@ export function CanvasWithTools() {
     }
 
     // Drawing
-    if (pointer.isDown && ['pencil', 'brush', 'eraser'].includes(activeTool)) {
+    if (pointer.isDown && ['pencil', 'brush', 'eraser', 'eyedropper'].includes(activeTool)) {
       const activeLayer = getActiveLayer();
       if (!activeLayer || !activeLayer.canvas) return;
 
@@ -225,7 +227,7 @@ export function CanvasWithTools() {
       return;
     }
 
-    if (pointer.isDown && ['pencil', 'brush', 'eraser', 'fill'].includes(activeTool)) {
+    if (pointer.isDown && ['pencil', 'brush', 'eraser', 'fill', 'eyedropper'].includes(activeTool)) {
       const activeLayer = getActiveLayer();
       if (!activeLayer || !activeLayer.canvas) return;