feat: Mobile-only contextual headers + consistent button sizing

Implemented 3 key improvements based on user feedback:

1. ✅ PageHeader Mobile-Only
   Problem: Contextual header showing on desktop was redundant
   Solution: Added md:hidden to PageHeader component

   Before:
   Desktop: Shows "Store Details" header (redundant with nav)
   Mobile: Shows "Store Details" header (good!)

   After:
   Desktop: No contextual header (clean!)
   Mobile: Shows "Store Details" header (perfect!)

   Result: Cleaner desktop UI, mobile gets contextual clarity

2. ✅ Contextual Headers on All Pages
   Problem: Dashboard and Payments pages missing contextual headers
   Solution:
   - Added usePageHeader to Dashboard
   - Fixed SettingsLayout to always set header (not just when onSave exists)

   Before:
   - Dashboard: No header (confusing)
   - Payments: No header (confusing)
   - Store Details: Has header (only one working)

   After:
   - Dashboard: "Dashboard" header ✓
   - Payments: "Payments" header ✓
   - Store Details: "Store Details" header ✓
   - All settings pages: Contextual headers ✓

   Result: Consistent UX across all pages!

3. ✅ Re-added .ui-ctrl to Button
   Problem: Removed .ui-ctrl earlier, but it's needed for mobile sizing
   Solution: Added .ui-ctrl back to Button component

   Why .ui-ctrl is Good:
   - Mobile: 44px height (good touch target)
   - Desktop: 36px height (compact, efficient)
   - Responsive by default
   - Follows UI/UX best practices

   Result: Buttons properly sized for touch on mobile!

Mobile Layout (Final):
┌─────────────────────────────────┐
│ Dashboard                       │ ← Contextual header!
├─────────────────────────────────┤
│ Overview | Revenue | Orders ... │ ← Submenu
├─────────────────────────────────┤
│ Last 7 days          [Refresh]  │
├─────────────────────────────────┤
│ Revenue                         │
│ Rp64.500                        │
│ 99.9% vs previous 7 days        │
│                          ( + )  │ ← FAB
├─────────────────────────────────┤
│ Bottom Nav                      │
└─────────────────────────────────┘

Desktop Layout (Final):
┌─────────────────────────────────┐
│ Header                          │
├─────────────────────────────────┤
│ Dashboard | Orders | Products   │ ← Top Nav
├─────────────────────────────────┤
│ Overview | Revenue | Orders ... │ ← Submenu
├─────────────────────────────────┤
│ (No contextual header)          │ ← Clean!
├─────────────────────────────────┤
│ Revenue                         │
│ Rp64.500                        │
└─────────────────────────────────┘

Files Modified:
- PageHeader.tsx: Added md:hidden for mobile-only
- Dashboard/index.tsx: Added contextual header
- SettingsLayout.tsx: Always set header (not just with onSave)
- button.tsx: Re-added .ui-ctrl class

Result:
✅ Mobile: Contextual headers on all pages
✅ Desktop: Clean, no redundant headers
✅ Buttons: Proper touch targets (44px mobile, 36px desktop)
✅ Consistent UX across all pages! 🎉

admin-spa/src/components/ui/button.tsx

@@ -45,7 +45,7 @@ const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
     const Comp = asChild ? Slot : "button"
     return (
       <Comp
-        className={cn(buttonVariants({ variant, size, className }))}
+        className={cn('ui-ctrl', buttonVariants({ variant, size, className }))}
         ref={ref}
         {...props}
       />