fix: Sticky submenu + emoji flags instead of images

1. Made Settings Submenu Sticky ✅
   Problem: Settings submenu wasn't sticky like Dashboard
   Solution: Added sticky positioning to SubmenuBar

   Added classes:
   - sticky top-0 z-20
   - bg-background/95 backdrop-blur
   - supports-[backdrop-filter]:bg-background/60

   Result: ✅ Settings submenu now stays at top when scrolling

2. Switched to Emoji Flags ✅
   Problem: Base64 images not showing in select options
   Better Solution: Use native emoji flags

   Benefits:
   - ✅ No image loading required
   - ✅ Native OS rendering
   - ✅ Smaller bundle size
   - ✅ Better performance
   - ✅ Always works (no broken images)

   Implementation:
   function countryCodeToEmoji(countryCode: string): string {
     const codePoints = countryCode
       .toUpperCase()
       .split('')
       .map(char => 127397 + char.charCodeAt(0));
     return String.fromCodePoint(...codePoints);
   }

   // AE → 🇦🇪
   // US → 🇺🇸
   // ID → 🇮🇩

3. Updated Currency Select ✅
   Before: [Image] United Arab Emirates dirham (AED)
   After:  🇦🇪 United Arab Emirates dirham (AED)

   - Emoji flag in label
   - No separate icon prop needed
   - Works immediately

4. Updated Store Summary ✅
   Before: [Image] Your store is located in Indonesia
   After:  🇮🇩 Your store is located in Indonesia

   - Dynamic emoji flag based on currency
   - Cleaner implementation
   - No image loading

5. Simplified SearchableSelect ✅
   - Removed icon prop (not needed with emoji)
   - Removed image rendering code
   - Simpler component API

Files Modified:
- SubmenuBar.tsx: Added sticky positioning
- Store.tsx: Emoji flags + helper function
- searchable-select.tsx: Removed icon support

Why Emoji > Images:
✅ Universal support (all modern browsers/OS)
✅ No loading time
✅ No broken images
✅ Smaller code
✅ Native rendering
✅ Accessibility friendly

admin-spa/src/components/nav/SubmenuBar.tsx

@@ -12,7 +12,7 @@ export default function SubmenuBar({ items = [] }: Props) {
   if (items.length === 0) return null;
 
   return (
-    <div data-submenubar className="border-b border-border bg-background/95">
+    <div data-submenubar className="border-b border-border bg-background md:bg-background/95 md:backdrop-blur md:supports-[backdrop-filter]:bg-background/60 sticky top-0 z-20">
       <div className="px-4 py-2">
         <div className="flex gap-2 overflow-x-auto no-scrollbar">
           {items.map((it) => {