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/components/register-form.tsx

@@ -84,6 +84,25 @@ export function RegisterForm() {
               />
             </div>
           </div>
+          <div className="mt-4">
+            <label
+              className="mb-3 mt-5 block text-xs font-medium text-gray-900"
+              htmlFor="confirmPassword"
+            >
+              {t('auth.confirmPassword')}
+            </label>
+            <div className="relative">
+              <Input
+                className="peer block w-full rounded-md border border-gray-200 py-[9px] pl-10 text-sm outline-2 placeholder:text-gray-500"
+                id="confirmPassword"
+                type="password"
+                name="confirmPassword"
+                placeholder={t('auth.confirmPasswordPlaceholder')}
+                required
+                minLength={6}
+              />
+            </div>
+          </div>
         </div>
         <RegisterButton />
         <div