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/components/dashboard-view.tsx

@@ -519,7 +519,7 @@ export function DashboardView({ onNoteSelect }: DashboardViewProps) {
     try {
       const res = await fetch('/api/ai/echo')
       const json = await res.json()
-      if (res.status === 403 && json.error === 'ai_consent_required') { await requestAiConsent(); return }
+      if (res.status === 403 && json.code === 'ai_consent_required') { await requestAiConsent(); return }
       if (!res.ok) throw new Error(json.error)
       if (json.insight) {
         await reloadBriefingAndPaths()