fix: enlarge shirt print area for more realistic sizing

Design box expanded from 370x370 to 500x450 and repositioned
higher on the chest for typical t-shirt print proportions.

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

backend/app/api/designs.py

@@ -23,7 +23,7 @@ settings = get_settings()
 MOCKUP_TEMPLATES = {
     "shirt": {
         "template": "shirt-template.png",
-        "design_box": (330, 310, 370, 370),  # x, y, w, h — chest area on black tee
+        "design_box": (262, 230, 500, 450),  # x, y, w, h — chest area on black tee
         "blend": "screen",  # screen blend for light designs on dark fabric
     },
     "sticker": {

frontend/lib/mockups.ts

@@ -12,7 +12,7 @@ export interface MockupConfig {
 export const MOCKUP_CONFIGS: MockupConfig[] = [
   {
     template: "/mockups/shirt-template.png",
-    designArea: { x: 330, y: 310, width: 370, height: 370 },
+    designArea: { x: 262, y: 230, width: 500, height: 450 },
     label: "T-Shirt",
     productType: "shirt",
     price: 29.99,