feat(billing): implement US-3.7 billing and subscription UX with detailed dashboard, real-time invoice history, inline paywall and upgrade confirmation

memento-note/app/api/billing/invoices/route.ts

@@ -0,0 +1,40 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { auth } from '@/auth';
+import { stripe } from '@/lib/stripe';
+import { prisma } from '@/lib/prisma';
+
+export async function GET(req: NextRequest) {
+  const session = await auth();
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+
+  const userId = session.user.id;
+
+  try {
+    const subscription = await prisma.subscription.findUnique({ where: { userId } });
+    if (!subscription?.stripeCustomerId) {
+      return NextResponse.json([]);
+    }
+
+    const invoices = await stripe.invoices.list({
+      customer: subscription.stripeCustomerId,
+      limit: 50,
+    });
+
+    const formattedInvoices = invoices.data.map((invoice) => ({
+      id: invoice.id,
+      number: invoice.number,
+      amount: invoice.amount_paid || invoice.total,
+      currency: invoice.currency,
+      status: invoice.status, // 'paid', 'open', 'draft', 'uncollectible', 'void'
+      date: invoice.created, // timestamp en secondes
+      pdfUrl: invoice.invoice_pdf,
+    }));
+
+    return NextResponse.json(formattedInvoices);
+  } catch (error) {
+    console.error('[billing/invoices]', error);
+    return NextResponse.json({ error: 'Failed to fetch invoices' }, { status: 500 });
+  }
+}

memento-note/app/api/billing/status/route.ts

@@ -22,6 +22,7 @@ export async function GET() {
       effectiveTier,
       status,
       currentPeriodEnd: currentPeriodEnd ?? null,
+      currentPeriodStart: subscription?.currentPeriodStart ?? null,
       cancelAtPeriodEnd: subscription?.cancelAtPeriodEnd ?? false,
       hasStripeSubscription: !!subscription?.stripeSubscriptionId,
     });