feat(07-06): settings-api client + SmtpSettingsForm + SMTP page (DKV-05)

- settings-api.ts: fetchSmtp/saveSmtp/testSmtp with credentials:'include'; SmtpConfig exposes only hasPassword (T-07-17)
- smtp-settings-form.tsx: Surface C form with show/hide password toggle, test-feedback auto-clears 6s
- settings/general/smtp/page.tsx: SmtpSettingsPage heading + SmtpSettingsForm
- de.json + en.json: add smtp.showPassword/hidePassword/testTesting/testSuccess/testFailed keys
- TDD GREEN: 5/5 tests pass; aria-hidden* on required markers removed for correct getByLabelText matching

apps/web/src/app/(portal)/settings/general/smtp/page.tsx

@@ -0,0 +1,22 @@
+'use client';
+
+import { useTranslations } from 'next-intl';
+import { SmtpSettingsForm } from '@/components/settings/smtp-settings-form';
+
+/**
+ * SMTP settings page — /settings/general/smtp (Surface C, DKV-05).
+ * Sits inside the existing settings layout (SettingsSidebar wraps it).
+ * Heading follows the settings/dashboard/page.tsx pattern exactly.
+ */
+export default function SmtpSettingsPage() {
+  const t = useTranslations('settings');
+
+  return (
+    <div>
+      <h1 className="mb-6 text-lg font-semibold text-foreground">
+        {t('smtp.title')}
+      </h1>
+      <SmtpSettingsForm />
+    </div>
+  );
+}