feat: add orientation indicators to debug panel

- Display UP/DOWN/LEFT/RIGHT labels at canvas edges
- Shows which direction is which in the original image
- Helps verify rotation correctness visually

frontend/components/DebugRotationPanel.tsx

@@ -95,6 +95,22 @@ export function DebugRotationPanel({
     // Save state
     ctx.save();
 
+    // Draw orientation indicators at corners
+    ctx.fillStyle = 'rgba(255, 255, 255, 0.9)';
+    ctx.font = 'bold 14px monospace';
+    ctx.textAlign = 'left';
+    ctx.textBaseline = 'top';
+    ctx.fillText('⬆ UP', 10, 5);
+    ctx.fillText('⬅ LEFT', 5, 20);
+
+    ctx.textAlign = 'right';
+    ctx.textBaseline = 'top';
+    ctx.fillText('RIGHT ➡', canvas.width - 10, 20);
+
+    ctx.textAlign = 'left';
+    ctx.textBaseline = 'bottom';
+    ctx.fillText('⬇ DOWN', 10, canvas.height - 5);
+
     // Draw crop bounds rectangle (bright green)
     ctx.strokeStyle = '#00FF00';
     ctx.lineWidth = 4;