feat(credits): solde IA unique (option M), packs Stripe et polish billing

Un pot de crédits global (BASIC 100 / PRO 1 000 / BUSINESS 4 000) remplace
les seaux par fonction côté débit. Packs one-shot S/M/L, admin sans seaux
legacy, usage multi-features, hints de coût, anti-flash thème et hydratation
admin. Inclut aussi le pipeline slides renforcé et la page publique polishée.

memento-note/prisma/migrations/20260716190000_add_ai_credit_tables/migration.sql

@@ -0,0 +1,55 @@
+-- Crédits IA globaux (modèle A) — tables additives uniquement
+CREATE TABLE IF NOT EXISTS "AiCreditAccount" (
+    "id" TEXT NOT NULL,
+    "userId" TEXT NOT NULL,
+    "periodKey" TEXT NOT NULL,
+    "subscriptionGranted" INTEGER NOT NULL DEFAULT 0,
+    "subscriptionSpent" INTEGER NOT NULL DEFAULT 0,
+    "purchasedBalance" INTEGER NOT NULL DEFAULT 0,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "AiCreditAccount_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS "AiCreditAccount_userId_key" ON "AiCreditAccount"("userId");
+CREATE INDEX IF NOT EXISTS "AiCreditAccount_periodKey_idx" ON "AiCreditAccount"("periodKey");
+
+CREATE TABLE IF NOT EXISTS "AiCreditLedger" (
+    "id" TEXT NOT NULL,
+    "userId" TEXT NOT NULL,
+    "kind" TEXT NOT NULL,
+    "amount" INTEGER NOT NULL,
+    "feature" TEXT,
+    "balanceAfter" INTEGER,
+    "metadata" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "AiCreditLedger_pkey" PRIMARY KEY ("id")
+);
+
+CREATE INDEX IF NOT EXISTS "AiCreditLedger_userId_createdAt_idx" ON "AiCreditLedger"("userId", "createdAt");
+CREATE INDEX IF NOT EXISTS "AiCreditLedger_userId_feature_createdAt_idx" ON "AiCreditLedger"("userId", "feature", "createdAt");
+CREATE INDEX IF NOT EXISTS "AiCreditLedger_userId_kind_createdAt_idx" ON "AiCreditLedger"("userId", "kind", "createdAt");
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint WHERE conname = 'AiCreditAccount_userId_fkey'
+  ) THEN
+    ALTER TABLE "AiCreditAccount"
+      ADD CONSTRAINT "AiCreditAccount_userId_fkey"
+      FOREIGN KEY ("userId") REFERENCES "User"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+  END IF;
+END $$;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint WHERE conname = 'AiCreditLedger_userId_fkey'
+  ) THEN
+    ALTER TABLE "AiCreditLedger"
+      ADD CONSTRAINT "AiCreditLedger_userId_fkey"
+      FOREIGN KEY ("userId") REFERENCES "User"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+  END IF;
+END $$;

memento-note/prisma/schema.prisma

@@ -60,6 +60,8 @@ model User {
   flashcardDecks        FlashcardDeck[]
   errorLogs             ErrorLog[]
   gmailScanHistory      GmailScanHistory[]
+  aiCreditAccount       AiCreditAccount?
+  aiCreditLedger        AiCreditLedger[]
 }
 
 model Account {
@@ -890,6 +892,49 @@ model PlanEntitlement {
   @@index([tier])
 }
 
+// ===== CRÉDITS IA GLOBAUX (modèle A) =====
+
+/// Solde de crédits par utilisateur pour la période mensuelle en cours.
+model AiCreditAccount {
+  id                   String   @id @default(cuid())
+  userId               String   @unique
+  /// Clé de période YYYY-MM
+  periodKey            String
+  /// Allocation abonnement du mois (ex. 300 pour PRO)
+  subscriptionGranted  Int      @default(0)
+  /// Crédits d'abonnement déjà consommés ce mois
+  subscriptionSpent    Int      @default(0)
+  /// Crédits de packs achetés encore disponibles (reportables)
+  purchasedBalance     Int      @default(0)
+  updatedAt            DateTime @updatedAt
+  createdAt            DateTime @default(now())
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@index([periodKey])
+}
+
+/// Journal immuable des mouvements de crédits (transparence d'usage).
+model AiCreditLedger {
+  id          String   @id @default(cuid())
+  userId      String
+  /// GRANT_SUBSCRIPTION | PURCHASE_PACK | CONSUME | RELEASE | ADMIN_ADJUST | EXPIRE_SUBSCRIPTION | ADMIN_RESET
+  kind        String
+  /// Positif = crédit, négatif = débit
+  amount      Int
+  /// Feature technique pour le tableau de répartition (ex. slide_generate)
+  feature     String?
+  balanceAfter Int?
+  metadata    String?
+  createdAt   DateTime @default(now())
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@index([userId, createdAt])
+  @@index([userId, feature, createdAt])
+  @@index([userId, kind, createdAt])
+}
+
 // ===== CLUSTERING & BRIDGE NOTES =====
 
 model NoteCluster {