feat: language selector on user creation, pass to welcome email

Adds preferred_language field to Users, language picker (EN/AR) in
create/edit user form, persists to NocoDB, and passes it to the
welcome notification so new users receive emails in their language.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src/i18n/ar.json

@@ -570,6 +570,7 @@
   "users.passwordMismatch": "كلمات المرور غير متطابقة",
   "users.passwordRequired": "كلمة المرور مطلوبة للمستخدمين الجدد",
   "users.saveFailed": "فشل في حفظ المستخدم",
+  "users.preferredLanguage": "اللغة المفضلة",
   "users.deleteFailed": "فشل في حذف المستخدم",
 
   "settings.saveFailed": "فشل في الحفظ",

client/src/i18n/en.json

@@ -570,6 +570,7 @@
   "users.passwordMismatch": "Passwords do not match",
   "users.passwordRequired": "Password is required for new users",
   "users.saveFailed": "Failed to save user",
+  "users.preferredLanguage": "Preferred Language",
   "users.deleteFailed": "Failed to delete user",
 
   "settings.saveFailed": "Failed to save",

client/src/pages/Users.jsx

@@ -14,7 +14,7 @@ const ROLES = [
 ]
 
 const EMPTY_FORM = {
-  name: '', email: '', password: '', role: 'contributor', avatar: '',
+  name: '', email: '', password: '', role: 'contributor', avatar: '', preferred_language: 'en',
 }
 
 function RoleBadge({ role }) {
@@ -66,6 +66,7 @@ export default function Users() {
         email: form.email,
         role: form.role,
         avatar: form.avatar || null,
+        preferred_language: form.preferred_language || 'en',
       }
       if (form.password) data.password = form.password
 
@@ -97,6 +98,7 @@ export default function Users() {
       password: '',
       role: user.role || 'contributor',
       avatar: user.avatar || '',
+      preferred_language: user.preferred_language || 'en',
     })
     setConfirmPassword('')
     setPasswordError('')
@@ -312,6 +314,27 @@ export default function Users() {
             </div>
           </div>
 
+          <div>
+            <label className="block text-sm font-medium text-text-primary mb-1">{t('users.preferredLanguage')}</label>
+            <div className="grid grid-cols-2 gap-2">
+              {[{ value: 'en', label: 'English', flag: '🇬🇧' }, { value: 'ar', label: 'العربية', flag: '🇸🇦' }].map(l => (
+                <button
+                  key={l.value}
+                  type="button"
+                  onClick={() => setForm(f => ({ ...f, preferred_language: l.value }))}
+                  className={`p-2.5 rounded-lg border-2 text-center transition-all ${
+                    form.preferred_language === l.value
+                      ? 'border-brand-primary bg-brand-primary/5'
+                      : 'border-border hover:border-brand-primary/30'
+                  }`}
+                >
+                  <span className="text-lg">{l.flag}</span>
+                  <span className="text-xs font-medium text-text-primary ms-1.5">{l.label}</span>
+                </button>
+              ))}
+            </div>
+          </div>
+
           <div className="flex items-center justify-end gap-3 pt-4 border-t border-border">
             <button
               onClick={() => { setShowModal(false); setEditingUser(null) }}