feat: implement Phase 10 - Shape Tools

Add comprehensive shape drawing system with support for 7 shape types:
rectangle, ellipse, line, arrow, polygon, star, and triangle.

Features:
- Created types/shape.ts with ShapeType and ShapeSettings interfaces
- Implemented lib/shape-utils.ts with drawing algorithms for all shapes:
  * Rectangle with optional corner radius
  * Ellipse with independent x/y radii
  * Line with stroke support
  * Arrow with configurable head size and angle
  * Polygon with adjustable sides (3-20)
  * Star with points and inner radius control
  * Triangle (equilateral style)
- Created store/shape-store.ts for shape state management
- Implemented tools/shape-tool.ts as unified tool handling all shapes
- Built components/shapes/shape-panel.tsx with comprehensive UI:
  * Grid selector for all 7 shape types
  * Fill/stroke toggles with color pickers
  * Dynamic properties panel (corner radius, sides, inner radius, etc.)
  * Real-time stroke width adjustment
- Integrated ShapeTool into canvas-with-tools.tsx
- Added ShapePanel to editor-layout.tsx sidebar
- Removed duplicate ShapeType/ShapeSettings from types/tool.ts

All shapes support:
- Fill with color selection
- Stroke with color and width controls
- Shape-specific properties (corners, sides, arrow heads, etc.)
- Undo/redo via DrawCommand integration

Build Status: ✓ Successful (1290ms)

🤖 Generated with Claude Code

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

components/editor/editor-layout.tsx

@@ -12,6 +12,7 @@ import { ColorPanel } from '@/components/colors';
 import { FilterPanel } from '@/components/filters';
 import { SelectionPanel } from '@/components/selection';
 import { TransformPanel } from '@/components/transform';
+import { ShapePanel } from '@/components/shapes';
 import { useKeyboardShortcuts } from '@/hooks/use-keyboard-shortcuts';
 import { useFileOperations } from '@/hooks/use-file-operations';
 import { useDragDrop } from '@/hooks/use-drag-drop';
@@ -187,6 +188,9 @@ export function EditorLayout() {
         {/* Transform Panel */}
         <TransformPanel />
 
+        {/* Shape Panel */}
+        <ShapePanel />
+
         {/* Canvas area */}
         <div className="flex-1">
           <CanvasWithTools />