feat: add password confirmation to register + fix i18n hardcoded strings

- Add confirmPassword field to registration form with Zod validation
- Replace ~30 hardcoded French/English strings in admin-settings-form
  with proper t() i18n calls (Ollama models, Custom models, search test)
- Extract SettingsHeader to client component for i18n support
- Add 15 i18n keys to all 15 locale files (auth + admin.ai + admin.tools)
- Remove debug "Config value" line from embeddings section

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/app/(admin)/admin/settings/settings-header.tsx

@@ -0,0 +1,17 @@
+'use client'
+
+import { useLanguage } from '@/lib/i18n'
+
+export function SettingsHeader() {
+  const { t } = useLanguage()
+  return (
+    <div>
+      <h1 className="text-3xl font-bold text-gray-900 dark:text-white">
+        {t('admin.settings')}
+      </h1>
+      <p className="text-gray-600 dark:text-gray-400 mt-1">
+        {t('admin.settingsDescription')}
+      </p>
+    </div>
+  )
+}