fix: password minLength 6 -> 8 to match backend validation

frontend/src/app/auth/register/page.tsx

@@ -51,7 +51,7 @@ export default function RegisterPage() {
           onChange={(e) => setPassword(e.target.value)}
           className="w-full rounded-lg border border-white/10 bg-white/5 px-4 py-3 text-white placeholder-white/40 outline-none focus:border-green-500"
           required
-          minLength={6}
+          minLength={8}
         />
 
         <select

frontend/src/components/RegisterModal.tsx

@@ -47,7 +47,7 @@ export default function RegisterModal({ onClose }: { onClose: () => void }) {
           onChange={(e) => setPassword(e.target.value)}
           className="w-full rounded-lg border border-white/10 bg-white/5 px-4 py-3 text-white placeholder-white/40 outline-none focus:border-green-500"
           required
-          minLength={6}
+          minLength={8}
         />
 
         <select