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/lib/consent/server-consent.ts

@@ -25,6 +25,19 @@ export async function hasUserAiConsent(): Promise<boolean> {
   return settings?.aiProcessingConsent ?? false
 }
 
-export function aiConsentForbiddenResponse() {
-  return NextResponse.json({ error: 'ai_consent_required' }, { status: 403 })
+const DEFAULT_AI_CONSENT_MESSAGE = 'AI processing consent is required to use this feature.'
+const AI_CONSENT_ERROR_KEY = 'consent.ai.requiredToast'
+
+export function aiConsentForbiddenResponse(message?: string) {
+  return NextResponse.json(
+    { error: message ?? DEFAULT_AI_CONSENT_MESSAGE, code: 'ai_consent_required', errorKey: AI_CONSENT_ERROR_KEY },
+    { status: 403 }
+  )
+}
+
+export function aiConsentForbiddenJson(message?: string) {
+  return NextResponse.json(
+    { success: false, error: message ?? DEFAULT_AI_CONSENT_MESSAGE, code: 'ai_consent_required', errorKey: AI_CONSENT_ERROR_KEY },
+    { status: 403 }
+  )
 }