fix: Reactive store name in header + sticky header positioning

1. Store Name Updates in Header ✅

   Problem: Changing store name doesn't update topbar title
   Solution: Custom event system

   Flow:
   - User saves store settings
   - Dispatch 'woonoow:store:updated' event with store_name
   - Header component listens for event
   - Updates title in real-time

   Files:
   - App.tsx: useState + useEffect listener
   - Store.tsx: Dispatch event on save success

2. Sticky Header Positioning ✅

   Problem 1: Sticky header hidden under submenu
   Solution: top-[49px] instead of top-0

   Problem 2: Sticky header not edge-to-edge
   Solution: Negative margins to break out of container

   Before:
   <div className="sticky top-0 ...">
     <div className="container ...">

   After:
   <div className="sticky top-[49px] -mx-4 px-4 lg:-mx-6 lg:px-6">
     <div className="container ...">

   Responsive:
   - Mobile: -mx-4 px-4 (breaks out of 16px padding)
   - Desktop: -mx-6 px-6 (breaks out of 24px padding)

   Result:
   ✅ Sticky header below submenu (49px offset)
   ✅ Edge-to-edge background
   ✅ Content still centered in container
   ✅ Works in fullscreen, standalone, and wp-admin modes

3. Layout Structure

   Parent: space-y-6 lg:p-6 pb-6
   ├─ Sticky Header: -mx to break out, top-[49px]
   └─ Content: container max-w-5xl

   This ensures:
   - Sticky header spans full width
   - Content stays centered
   - Proper spacing maintained

Files Modified:
- App.tsx: Reactive site title
- Store.tsx: Dispatch update event
- SettingsLayout.tsx: Fixed sticky positioning

admin-spa/src/routes/Settings/Store.tsx

@@ -137,6 +137,11 @@ export default function StoreDetailsPage() {
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['store-settings'] });
       toast.success('Your store details have been updated successfully.');
+      
+      // Dispatch event to update site title in header
+      window.dispatchEvent(new CustomEvent('woonoow:store:updated', {
+        detail: { store_name: settings.storeName }
+      }));
     },
     onError: () => {
       toast.error('Failed to save store settings');