feat(billing): implement billing module with Stripe and Mercado Pago integration

- Add Stripe and Mercado Pago providers for handling subscriptions.
- Create billing repository and access services for managing billing records.
- Implement webhook handlers for processing events from Stripe and Mercado Pago.
- Add routes for checkout, canceling subscriptions, and retrieving billing status.
- Introduce billing status management with appropriate state transitions.
- Create tests for billing functionalities including webhook idempotency and provider resolution.
- Document the billing module architecture, environment variables, and API endpoints.

apps/backend/test/billing/duplicate-subscription.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it, mock } from 'bun:test';
+import { prismaMock } from '../support/prisma.mock';
+
+describe('duplicate-subscription', () => {
+  it('returns true when status is ACTIVE', async () => {
+    prismaMock.complexBilling.findUnique.mockResolvedValue({
+      status: 'ACTIVE',
+    } as never);
+
+    const { hasActiveSubscription } = await import(
+      '@/modules/billing/services/billing-repository.service'
+    );
+
+    const result = await hasActiveSubscription('complex-active');
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toBe(true);
+    }
+  });
+
+  it('returns true when status is TRIAL', async () => {
+    prismaMock.complexBilling.findUnique.mockResolvedValue({
+      status: 'TRIAL',
+    } as never);
+
+    const { hasActiveSubscription } = await import(
+      '@/modules/billing/services/billing-repository.service'
+    );
+
+    const result = await hasActiveSubscription('complex-trial');
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toBe(true);
+    }
+  });
+
+  it('returns false when status is CANCELED', async () => {
+    prismaMock.complexBilling.findUnique.mockResolvedValue({
+      status: 'CANCELED',
+    } as never);
+
+    const { hasActiveSubscription } = await import(
+      '@/modules/billing/services/billing-repository.service'
+    );
+
+    const result = await hasActiveSubscription('complex-canceled');
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toBe(false);
+    }
+  });
+
+  it('returns false when no billing record exists', async () => {
+    prismaMock.complexBilling.findUnique.mockResolvedValue(null as never);
+
+    const { hasActiveSubscription } = await import(
+      '@/modules/billing/services/billing-repository.service'
+    );
+
+    const result = await hasActiveSubscription('complex-no-billing');
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toBe(false);
+    }
+  });
+});