feat(cms): implement multi-language support across frontend and admin UI

apps/spa/src/components/Navbar.tsx

@@ -284,7 +284,7 @@ export default function Navbar({ categories = [], topOffsetClassName = 'top-0' }
               <div className="absolute top-full right-0 pt-3 w-36 opacity-0 pointer-events-none group-hover:opacity-100 group-hover:pointer-events-auto transition-all duration-300">
                 <div className="bg-white/95 backdrop-blur-xl border border-spa-stone/10 rounded-xl overflow-hidden shadow-xl p-1">
                   <div className="px-3 py-2 border-b border-spa-stone/10 mb-1">
-                    <p className="text-[10px] text-spa-stone/60 uppercase tracking-widest leading-tight truncate">Signed in as</p>
+                    <p className="text-[10px] text-spa-stone/60 uppercase tracking-widest leading-tight truncate">{t('nav.signedInAs', 'Signed in as')}</p>
                     <p className="text-xs text-spa-forest font-bold truncate">{customer.displayName}</p>
                   </div>
                   <Link 
@@ -297,7 +297,7 @@ export default function Navbar({ categories = [], topOffsetClassName = 'top-0' }
                     onClick={logoutLiff} 
                     className="w-full text-left px-3 py-2 text-xs uppercase tracking-widest text-rose-500 hover:text-rose-600 hover:bg-rose-50 rounded-lg transition-colors font-bold"
                   >
-                    Logout
+                    {t('nav.logout', 'Logout')}
                   </button>
                 </div>
               </div>
@@ -307,7 +307,7 @@ export default function Navbar({ categories = [], topOffsetClassName = 'top-0' }
               onClick={loginLiff}
               className="px-4 py-2 rounded-full text-xs font-bold uppercase tracking-widest bg-[#00B900] text-white hover:bg-[#009900] transition-all duration-300 shadow-sm"
             >
-              LINE Login
+              {t('nav.login', 'LINE Login')}
             </button>
           )}
         </div>
@@ -503,14 +503,14 @@ export default function Navbar({ categories = [], topOffsetClassName = 'top-0' }
                 onClick={() => { logoutLiff(); setMobileOpen(false); }}
                 className="block w-full py-3 glass text-center rounded-xl text-xs font-bold uppercase tracking-widest text-rose-400 hover:bg-rose-500/10 transition-colors border border-rose-500/20 mt-2"
               >
-                Logout
+                {t('nav.logout', 'Logout')}
               </button>
             ) : (
               <button
                 onClick={() => { loginLiff(); setMobileOpen(false); }}
                 className="block w-full py-3 glass text-center rounded-xl text-xs font-bold uppercase tracking-widest text-[#00B900] hover:bg-[#00B900]/10 transition-colors border border-[#00B900]/50 mt-2"
               >
-                Login with LINE
+                {t('nav.login', 'Login with LINE')}
               </button>
             )}
           </div>