feat(users): require password confirmation when creating an app user

Both create paths (Users > Add User page and the CreateUserModal used during
device onboarding) now have a Confirm Password field. A mismatch shows an
inline error and blocks the create call, so a typo can't silently become the
user's Firebase Auth password. The confirm value is client-side only and is
never sent to the backend.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/pages/bellcloud/users/UserForm.jsx

@@ -319,6 +319,7 @@ export default function UserForm() {
     quickSettingsPIN: '',
     password:         '',
   })
+  const [confirmPassword, setConfirmPassword] = useState('')
   const [uid,     setUid]     = useState('')
   const [loading, setLoading] = useState(false)
   const [saving,  setSaving]  = useState(false)
@@ -356,6 +357,10 @@ export default function UserForm() {
   const handleSubmit = async (e) => {
     e.preventDefault()
     setError('')
+    if (!isEdit && form.password !== confirmPassword) {
+      setError('Passwords do not match.')
+      return
+    }
     setSaving(true)
     try {
       if (isEdit) {
@@ -437,16 +442,28 @@ export default function UserForm() {
                 />
               </div>
               {!isEdit && (
-                <FormField
-                  label="Password"
-                  name="password"
-                  type="password"
-                  value={form.password}
-                  onChange={set('password')}
-                  required
-                  placeholder="Min. 6 characters"
-                  hint="Used to sign into the mobile app immediately — this creates the Firebase Auth account."
-                />
+                <div style={{ display: 'grid', gridTemplateColumns: '1fr 1fr', gap: 'var(--space-4)' }}>
+                  <FormField
+                    label="Password"
+                    name="password"
+                    type="password"
+                    value={form.password}
+                    onChange={set('password')}
+                    required
+                    placeholder="Min. 6 characters"
+                    hint="Used to sign into the mobile app immediately — this creates the Firebase Auth account."
+                  />
+                  <FormField
+                    label="Confirm Password"
+                    name="confirm_password"
+                    type="password"
+                    value={confirmPassword}
+                    onChange={(e) => setConfirmPassword(e.target.value)}
+                    required
+                    placeholder="Re-enter password"
+                    error={confirmPassword && form.password !== confirmPassword ? 'Passwords do not match.' : undefined}
+                  />
+                </div>
               )}
               <StatusToggle value={form.status} onChange={setVal('status')} />
             </div>