feat(notes): liens internes, onglet Réseau, living blocks et consentement IA

Rend les liens entre notes visibles et persistants (sync NoteLink au save, auto-save, graphe réseau rafraîchi), ajoute living blocks, Memory Echo, recherche globale, consentement IA explicite et consolide les prototypes design en architectural-grid.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/lib/consent/server-consent.ts

@@ -0,0 +1,30 @@
+import { auth } from '@/auth'
+import { prisma } from '@/lib/prisma'
+import { NextResponse } from 'next/server'
+
+/**
+ * Checks if the authenticated user has explicit GDPR AI processing consent.
+ * Persistent consent: UserAISettings.aiProcessingConsent
+ * Session-only consent: signed JWT claim (not client headers — GDPR-safe)
+ */
+export async function hasUserAiConsent(): Promise<boolean> {
+  const session = await auth()
+  if (!session?.user?.id) {
+    return false
+  }
+
+  if (session.aiSessionConsent === true) {
+    return true
+  }
+
+  const settings = await prisma.userAISettings.findUnique({
+    where: { userId: session.user.id },
+    select: { aiProcessingConsent: true },
+  })
+
+  return settings?.aiProcessingConsent ?? false
+}
+
+export function aiConsentForbiddenResponse() {
+  return NextResponse.json({ error: 'ai_consent_required' }, { status: 403 })
+}