feat: add shadcn/ui stack with 60 best practices

- Add shadcn.csv covering components, theming, forms, a11y
  - Update core.py to include shadcn stack
  - Sync to all workflow files and cli assets

.codex/skills/ui-ux-pro-max/scripts/core.py

@@ -67,7 +67,8 @@ STACK_CONFIG = {
     "svelte": {"file": "stacks/svelte.csv"},
     "swiftui": {"file": "stacks/swiftui.csv"},
     "react-native": {"file": "stacks/react-native.csv"},
-    "flutter": {"file": "stacks/flutter.csv"}
+    "flutter": {"file": "stacks/flutter.csv"},
+    "shadcn": {"file": "stacks/shadcn.csv"}
 }
 
 # Common columns for all stacks