fix: mobile menu now renders in front of hero banner video on mobile

- Moved mobile drawer (and AnimatePresence) out of <nav> into sibling in React fragment so its z-index is evaluated at root stacking context (was previously confined inside nav's z context).
- Raised mobile menu container to z-[9999], sliding panel to z-[10000].
- Bumped LanguageSwitcher backdrop/dropdown to z-[9998]/z-[9999] for when opened from inside mobile menu.
- Lowered hero video to z-0 and gradient to z-5 (true background).
- Nav back to z-[50] (still above normal content).
- This ensures the full mobile menu (hamburger + drawer + language dropdown when clicked inside it) always stacks above the mobile_banner video and is fully visible.

components/LanguageSwitcher.tsx

@@ -31,12 +31,12 @@ export default function LanguageSwitcher() {
         <>
           {/* Backdrop */}
           <div 
-            className="fixed inset-0 z-[1010]" 
+            className="fixed inset-0 z-[9998]" 
             onClick={() => setIsOpen(false)} 
           />
           
           {/* Dropdown */}
-          <div className="absolute right-0 top-full mt-2 z-[1020] w-44 rounded-2xl border border-[#c99a2e]/20 bg-[#fbf7ef] shadow-2xl overflow-hidden">
+          <div className="absolute right-0 top-full mt-2 z-[9999] w-44 rounded-2xl border border-[#c99a2e]/20 bg-[#fbf7ef] shadow-2xl overflow-hidden">
             {languages.map((lang) => (
               <button
                 key={lang.code}