Phase 2: Canvas Editor Core

Implements the core canvas editor with react-konva:

- Added dependencies: react-konva, konva, use-image
- DesignCanvas component: 300×300px Stage with T-shirt SVG overlay
- TShirtSVG component: Visual t-shirt outline with print zone indicator
- ImageElement: Draggable/resizable image with Transformer handles
- TextElement: Draggable/resizable text with Transformer handles
- useDesignEditor hook: Element CRUD, selection, reordering
- Keyboard shortcut: Delete/Backspace removes selected element
- Test image added on mount for Phase 2 verification

Canvas info bar shows: "Design Area: 15" × 15" • Export: 4500 × 4500px @ 300 DPI"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/components/canvas/TShirtSVG.jsx

@@ -0,0 +1,59 @@
+export function TShirtSVG({ size = 300 }) {
+  const padding = size * 0.1;
+  const innerSize = size - padding * 2;
+
+  return (
+    <svg
+      width={size}
+      height={size}
+      viewBox={`0 0 ${size} ${size}`}
+      style={{
+        position: 'absolute',
+        top: '50%',
+        left: '50%',
+        transform: 'translate(-50%, -50%)',
+        pointerEvents: 'none',
+        zIndex: 0,
+      }}
+    >
+      {/* T-shirt outline */}
+      <path
+        d={`
+          M ${padding} ${padding + innerSize * 0.15}
+          L ${padding + innerSize * 0.15} ${padding}
+          L ${size - padding - innerSize * 0.15} ${padding}
+          L ${size - padding} ${padding + innerSize * 0.15}
+          L ${size - padding} ${size - padding}
+          L ${padding} ${size - padding}
+          Z
+        `}
+        fill="none"
+        stroke="var(--border)"
+        strokeWidth="2"
+        strokeDasharray="4,4"
+      />
+      {/* Chest area indicator (design zone) */}
+      <rect
+        x={size * 0.3}
+        y={size * 0.25}
+        width={size * 0.4}
+        height={size * 0.35}
+        fill="none"
+        stroke="var(--accent)"
+        strokeWidth="1.5"
+        opacity="0.5"
+      />
+      {/* Label */}
+      <text
+        x={size / 2}
+        y={size * 0.45}
+        textAnchor="middle"
+        fill="var(--text-muted)"
+        fontSize="10"
+        fontFamily="var(--font-mono)"
+      >
+        Print Zone
+      </text>
+    </svg>
+  );
+}