SYS-18: add production deployment stack for karbe.cosmolan.fr (Stripe test)

- enable Next.js standalone output and add Docker/Caddy production stack
- add production env template and deployment runbook
- add healthcheck endpoint for container supervision
- fix existing lint/type blockers discovered during validation

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/app/api/health/route.ts

@@ -0,0 +1,7 @@
+import { NextResponse } from "next/server";
+
+export const runtime = "nodejs";
+
+export async function GET() {
+  return NextResponse.json({ status: "ok" });
+}

src/app/api/stripe/webhook/route.ts

@@ -97,11 +97,16 @@ async function handlePaymentIntentFailed(paymentIntent: Stripe.PaymentIntent) {
 }
 
 async function handleSubscriptionUpdated(subscription: Stripe.Subscription) {
+  const currentPeriodEnd =
+    subscription.items.data[0]?.current_period_end ??
+    subscription.trial_end ??
+    subscription.canceled_at;
+
   await prisma.subscription.upsert({
     where: { providerSubId: subscription.id },
     update: {
       status: mapStripeSubscriptionStatus(subscription.status),
-      renewedAt: fromStripeTimestamp(subscription.current_period_end),
+      renewedAt: fromStripeTimestamp(currentPeriodEnd),
       canceledAt: fromStripeTimestamp(subscription.canceled_at),
     },
     create: {
@@ -111,7 +116,7 @@ async function handleSubscriptionUpdated(subscription: Stripe.Subscription) {
       providerSubId: subscription.id,
       status: mapStripeSubscriptionStatus(subscription.status),
       startedAt: fromStripeTimestamp(subscription.start_date) ?? new Date(),
-      renewedAt: fromStripeTimestamp(subscription.current_period_end),
+      renewedAt: fromStripeTimestamp(currentPeriodEnd),
       canceledAt: fromStripeTimestamp(subscription.canceled_at),
     },
   });