fix: replace raw ai_consent_required code with translatable message and consent prompt

- Centralize AI consent 403 responses in server-consent helpers
- Return human-readable message + code + i18n errorKey from all AI APIs
- Update dashboard and AI clients to detect code/errorKey and translate
- Add consent.ai.requiredToast i18n keys (fr/en)

memento-note/app/api/ai/title-suggestions/route.ts

@@ -7,7 +7,7 @@ import { getAISettings } from '@/app/actions/ai-settings'
 import { reserveAiUsageOrThrow } from '@/lib/ai-quota'
 import { QuotaExceededError, QuotaServiceUnavailableError } from '@/lib/entitlements'
 import { z } from 'zod'
-import { hasUserAiConsent } from '@/lib/consent/server-consent'
+import { hasUserAiConsent, aiConsentForbiddenResponse } from '@/lib/consent/server-consent'
 
 const requestSchema = z.object({
   content: z.string().min(1, "Le contenu ne peut pas être vide"),
@@ -37,7 +37,7 @@ export async function POST(req: NextRequest) {
 
     // GDPR AI Consent check
     if (!(await hasUserAiConsent())) {
-      return NextResponse.json({ error: 'ai_consent_required' }, { status: 403 })
+      return aiConsentForbiddenResponse()
     }
 
     const settings = await getAISettings(session.user.id)