feat(login): add LOGIN_SHOW_TOTP and LOGIN_SHOW_VERSION config flags

Two opt-out branding/login flags, both default true (no behaviour change
for existing deployments):

- LOGIN_SHOW_TOTP=false hides the manual "I have a 2FA code" toggle on the
  login form. Deployments that delegate auth to an external directory
  (LDAP/OIDC) where 2FA lives in the IdP have no server-side TOTP, so the
  toggle only ever leads to a failed login. Server-required TOTP
  (totp_required, which auto-shows the field) is unaffected.
- LOGIN_SHOW_VERSION=false hides the build version in the login footer, so
  the exact version isn't disclosed to unauthenticated visitors.

Wired through the existing config registry (CONFIG_ENV_MAP) → /api/config →
useConfig, matching the surrounding LOGIN_* options.

Refs #519.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/(main)/[locale]/login/page.tsx

@@ -133,7 +133,7 @@ export default function LoginPage() {
   const isMobileHandoff = Boolean(mobileRedirectUri);
   const { login, loginDemo, isLoading, error, clearError, isAuthenticated } = useAuthStore();
   const { theme, setTheme, initializeTheme } = useThemeStore(useShallow((s) => ({ theme: s.theme, setTheme: s.setTheme, initializeTheme: s.initializeTheme })));
-  const { appName, jmapServerUrl: configuredServerUrl, oauthEnabled, oauthOnly, oauthClientId: globalOauthClientId, oauthIssuerUrl: globalOauthIssuerUrl, oauthScopes, rememberMeEnabled, devMode, demoMode, loginLogoLightUrl, loginLogoDarkUrl, loginCompanyName, loginImprintUrl, loginPrivacyPolicyUrl, loginWebsiteUrl, isLoading: configLoading, error: configError, autoSsoEnabled, embeddedMode: _embeddedMode, allowCustomJmapEndpoint, jmapServers, jmapServerAutoPickByDomain } = useConfig();
+  const { appName, jmapServerUrl: configuredServerUrl, oauthEnabled, oauthOnly, oauthClientId: globalOauthClientId, oauthIssuerUrl: globalOauthIssuerUrl, oauthScopes, rememberMeEnabled, devMode, demoMode, loginLogoLightUrl, loginLogoDarkUrl, loginCompanyName, loginImprintUrl, loginPrivacyPolicyUrl, loginWebsiteUrl, loginShowTotp, loginShowVersion, isLoading: configLoading, error: configError, autoSsoEnabled, embeddedMode: _embeddedMode, allowCustomJmapEndpoint, jmapServers, jmapServerAutoPickByDomain } = useConfig();
   const resolvedTheme = useThemeStore((s) => s.resolvedTheme);
 
   const [formData, setFormData] = useState({
@@ -815,7 +815,7 @@ export default function LoginPage() {
                 )}
               </div>
             )}
-            <VersionBadge />
+            {loginShowVersion && <VersionBadge />}
           </div>
         </div>
       </div>
@@ -1142,8 +1142,12 @@ export default function LoginPage() {
                     </div>
                   </div>
 
-                  {/* 2FA toggle / field */}
+                  {/* 2FA toggle / field. The manual toggle can be hidden via
+                      LOGIN_SHOW_TOTP (loginShowTotp) for deployments whose mail
+                      server has no per-account TOTP (auth delegated to an
+                      external directory); server-required TOTP still shows. */}
                   {!showTotpField ? (
+                    loginShowTotp ? (
                     <button
                       type="button"
                       onClick={() => {
@@ -1155,6 +1159,7 @@ export default function LoginPage() {
                       <Shield className="w-3.5 h-3.5" />
                       {t("totp_toggle")}
                     </button>
+                    ) : null
                   ) : (
                     <div className="space-y-1.5">
                       <label htmlFor="totp" className="block text-sm font-medium text-foreground">
@@ -1349,7 +1354,7 @@ export default function LoginPage() {
               )}
             </div>
           )}
-          <VersionBadge />
+          {loginShowVersion && <VersionBadge />}
         </div>
       </div>
     </div>

app/api/config/route.ts

@@ -74,6 +74,8 @@ export async function GET(request: NextRequest) {
       loginImprintUrl: branded<string>('loginImprintUrl', ''),
       loginPrivacyPolicyUrl: branded<string>('loginPrivacyPolicyUrl', ''),
       loginWebsiteUrl: branded<string>('loginWebsiteUrl', ''),
+      loginShowTotp: configManager.get<boolean>('loginShowTotp', true),
+      loginShowVersion: configManager.get<boolean>('loginShowVersion', true),
       demoMode: configManager.get<boolean>('demoMode', false),
       allowCustomJmapEndpoint: configManager.get<boolean>('allowCustomJmapEndpoint', false),
       jmapServers: redactJmapServers(parseJmapServers(configManager.get<unknown>('jmapServers', []))),