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/actions/register.ts

@@ -9,7 +9,11 @@ import { getSystemConfig } from '@/lib/config';
 const RegisterSchema = z.object({
   email: z.string().email(),
   password: z.string().min(6),
+  confirmPassword: z.string().min(6),
   name: z.string().min(2),
+}).refine((data) => data.password === data.confirmPassword, {
+  message: 'Passwords do not match',
+  path: ['confirmPassword'],
 });
 
 export async function register(prevState: string | undefined, formData: FormData) {
@@ -24,6 +28,7 @@ export async function register(prevState: string | undefined, formData: FormData
   const validatedFields = RegisterSchema.safeParse({
     email: formData.get('email'),
     password: formData.get('password'),
+    confirmPassword: formData.get('confirmPassword'),
     name: formData.get('name'),
   });