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/echo/connections/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { auth } from '@/auth'
 import { memoryEchoService } from '@/lib/ai/services/memory-echo.service'
-import { hasUserAiConsent } from '@/lib/consent/server-consent'
+import { hasUserAiConsent, aiConsentForbiddenResponse } from '@/lib/consent/server-consent'
 
 /**
  * GET /api/ai/echo/connections?noteId={id}&page={page}&limit={limit}
@@ -19,10 +19,7 @@ export async function GET(req: NextRequest) {
     }
 
     if (!(await hasUserAiConsent())) {
-      return NextResponse.json(
-        { error: 'ai_consent_required' },
-        { status: 403 }
-      )
+      return aiConsentForbiddenResponse()
     }
 
     // Get query parameters

memento-note/app/api/ai/echo/fusion/route.ts

@@ -3,7 +3,7 @@ import { auth } from '@/auth'
 import { getChatProvider } from '@/lib/ai/factory'
 import { getSystemConfig } from '@/lib/config'
 import prisma from '@/lib/prisma'
-import { hasUserAiConsent } from '@/lib/consent/server-consent'
+import { hasUserAiConsent, aiConsentForbiddenResponse } from '@/lib/consent/server-consent'
 import { withAiQuota, handleQuotaHttpError } from '@/lib/ai-quota'
 
 /**
@@ -22,7 +22,7 @@ export async function POST(req: NextRequest) {
     }
 
     if (!(await hasUserAiConsent())) {
-      return NextResponse.json({ error: 'ai_consent_required' }, { status: 403 })
+      return aiConsentForbiddenResponse()
     }
 
     const body = await req.json()

memento-note/app/api/ai/echo/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { auth } from '@/auth'
 import { memoryEchoService } from '@/lib/ai/services/memory-echo.service'
-import { hasUserAiConsent } from '@/lib/consent/server-consent'
+import { hasUserAiConsent, aiConsentForbiddenResponse } from '@/lib/consent/server-consent'
 import { reserveUsageOrThrow, QuotaExceededError } from '@/lib/entitlements'
 
 /**
@@ -21,10 +21,7 @@ export async function GET(req: NextRequest) {
 
     // GDPR AI Consent check
     if (!(await hasUserAiConsent())) {
-      return NextResponse.json(
-        { error: 'ai_consent_required' },
-        { status: 403 }
-      )
+      return aiConsentForbiddenResponse()
     }
 
     // Get next insight (respects frequency limits)