feat: dashboard Second Brain, essai 7 jours et vérification e-mail

Rendre le dashboard actionnable (inbox, peek, carte mentale), aligner la facturation sur l’essai 7 jours, et bloquer le login e-mail tant que l’adresse n’est pas confirmée.

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

memento-note/lib/billing/trial.ts

@@ -0,0 +1,34 @@
+import { prisma } from '@/lib/prisma'
+
+export { SUBSCRIPTION_TRIAL_DAYS } from '@/lib/billing/trial-constants'
+
+/**
+ * Offer a trial only to users who never held a real Stripe subscription.
+ * Users with cus_mock / price_mock leftovers from local tests are still eligible
+ * if they never had a non-mock stripeSubscriptionId.
+ */
+export async function shouldOfferSubscriptionTrial(userId: string): Promise<boolean> {
+  const sub = await prisma.subscription.findUnique({
+    where: { userId },
+    select: {
+      stripeSubscriptionId: true,
+      tier: true,
+      status: true,
+      trialEndsAt: true,
+    },
+  })
+
+  if (!sub) return true
+
+  const stripeSubId = sub.stripeSubscriptionId
+  if (stripeSubId && !stripeSubId.startsWith('sub_mock')) {
+    return false
+  }
+
+  // Already on a paid / trial tier locally without a Stripe id (admin override)
+  if (sub.tier !== 'BASIC' && (sub.status === 'ACTIVE' || sub.status === 'TRIALING')) {
+    return false
+  }
+
+  return true
+}