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/app/api/billing/webhook/route.ts

@@ -6,11 +6,79 @@ import {
   handleSubscriptionDeleted,
   resolveUserIdFromStripeEvent,
 } from '@/lib/billing/sync-subscription-from-stripe';
-import { prisma } from '@/lib/prisma';
+import { addPurchasedCredits } from '@/lib/credits';
+import {
+  getCreditPack,
+  isCreditPackId,
+  resolvePackFromPriceId,
+} from '@/lib/billing/credit-packs';
 import type Stripe from 'stripe';
 
 export const runtime = 'nodejs';
 
+async function fulfillCreditPackPurchase(session: Stripe.Checkout.Session) {
+  if (session.mode !== 'payment') return;
+  if (session.payment_status && session.payment_status !== 'paid' && session.payment_status !== 'no_payment_required') {
+    console.warn('[billing/webhook] pack checkout not paid yet', session.id, session.payment_status);
+    return;
+  }
+
+  const userId = session.metadata?.userId as string | undefined;
+  if (!userId) {
+    console.warn('[billing/webhook] credit pack: no userId', session.id);
+    return;
+  }
+
+  let packId = session.metadata?.packId as string | undefined;
+  let credits = Number(session.metadata?.credits ?? 0);
+
+  if ((!packId || !Number.isFinite(credits) || credits <= 0) && session.line_items == null) {
+    try {
+      const full = await stripe.checkout.sessions.retrieve(session.id, {
+        expand: ['line_items.data.price'],
+      });
+      const priceId = full.line_items?.data?.[0]?.price?.id;
+      if (priceId) {
+        const resolved = await resolvePackFromPriceId(priceId);
+        if (resolved) {
+          packId = resolved.packId;
+          credits = resolved.credits;
+        }
+      }
+    } catch (err) {
+      console.error('[billing/webhook] expand line_items failed', err);
+    }
+  }
+
+  if (packId && isCreditPackId(packId) && (!Number.isFinite(credits) || credits <= 0)) {
+    credits = getCreditPack(packId).credits;
+  }
+
+  if (!Number.isFinite(credits) || credits <= 0) {
+    console.warn('[billing/webhook] credit pack: invalid credits', session.id, { packId, credits });
+    return;
+  }
+
+  const result = await addPurchasedCredits(userId, credits, {
+    stripeSessionId: session.id,
+    packId: packId ?? null,
+    type: 'credit_pack',
+    paymentIntent:
+      typeof session.payment_intent === 'string'
+        ? session.payment_intent
+        : session.payment_intent?.id ?? null,
+  });
+
+  if (result.applied) {
+    console.info('[billing/webhook] credited pack', {
+      userId,
+      credits: result.units,
+      packId,
+      sessionId: session.id,
+    });
+  }
+}
+
 export async function POST(req: NextRequest) {
   const body = await req.text();
   const headersList = await headers();
@@ -49,6 +117,11 @@ export async function POST(req: NextRequest) {
           } else {
             console.warn('[billing/webhook] checkout.session.completed: no userId in metadata', session.id);
           }
+        } else if (
+          session.mode === 'payment' &&
+          (session.metadata?.type === 'credit_pack' || session.metadata?.packId)
+        ) {
+          await fulfillCreditPackPurchase(session);
         }
         break;
       }