fix: 500 on setup complete + wizard shows all 7 steps

Two bugs:

1. AttributeError: AuthManager.update_password does not exist — the
   fallback when create_user fails should call set_password_admin().
   This caused a 500 on every setup submit when an admin user already
   existed (e.g. from a previous install attempt).

2. Wizard was jumping to step 2 and skipping domain steps 3-4 when
   preconfigured data existed in cell_config.json. Since the installer
   no longer sets that data, and the wizard must always show all steps,
   the installerConfigured state and all step-skipping navigation is
   removed. Values are still pre-filled if found in config.

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

webui/src/pages/Setup.jsx

@@ -831,10 +831,7 @@ export default function Setup() {
   const [submitting, setSubmitting] = useState(false);
   const [submitError, setSubmitError] = useState('');
 
-  // True when the bash installer already configured cell identity
-  const [installerConfigured, setInstallerConfigured] = useState(false);
-
-  // Pre-fill from installer config; if cell + domain already set, jump to password step
+  // Pre-fill from any existing config (e.g. from a previous partial run)
   useEffect(() => {
     setupAPI.getStatus()
       .then(res => {
@@ -849,12 +846,8 @@ export default function Setup() {
         if (pre.domain_name)          setCustomDomain(pre.domain_name);
         if (pre.cloudflare_api_token) setCloudflareToken(pre.cloudflare_api_token);
         if (pre.duckdns_token)        setDuckdnsToken(pre.duckdns_token);
-        if (pre.cell_name && pre.domain_mode) {
-          setInstallerConfigured(true);
-          setStep(2); // skip cell name + domain steps — already done by installer
-        }
       })
-      .catch(() => {}); // fail silently — wizard works from scratch
+      .catch(() => {});
   }, []);
 
   const skipStep4 = domainType === 'lan';
@@ -862,13 +855,9 @@ export default function Setup() {
   const goNext = () => setStep(s => Math.min(s + 1, TOTAL_STEPS));
   const goBack = () => setStep(s => Math.max(s - 1, 1));
 
-  // When installer pre-configured identity: step 2 → step 5 (skip domain steps)
-  const handleStep2Next = () => installerConfigured ? setStep(5) : goNext();
-  const handleStep2Back = () => installerConfigured ? setStep(1) : goBack();
-
   const handleStep3Next = () => skipStep4 ? setStep(5) : setStep(4);
   const handleStep4Back = () => setStep(3);
-  const handleStep5Back = () => installerConfigured ? setStep(2) : skipStep4 ? setStep(3) : setStep(4);
+  const handleStep5Back = () => skipStep4 ? setStep(3) : setStep(4);
 
   const handleSubmit = async () => {
     setSubmitError('');
@@ -949,8 +938,8 @@ export default function Setup() {
             confirm={passwordConfirm}
             onChangePassword={setPassword}
             onChangeConfirm={setPasswordConfirm}
-            onNext={handleStep2Next}
-            onBack={handleStep2Back}
+            onNext={goNext}
+            onBack={goBack}
           />
         )}
         {step === 3 && (