feat(F-001): scaffold modular monolith skeleton with boundary checker

- TypeScript + Fastify skeleton under project/ (src/modules, shared, infrastructure, app)
- scripts/check-module-boundaries.mjs enforcing module public-API rules (tested with fixtures)
- GET /health endpoint, error envelope without stack leakage
- specs/F-001-scaffold (SPEC/DESIGN/TASKS/TESTS), spec/tech.md dependency justification
- 30-ticket MercadoDeVida roadmap in backlog/features.json, spec/roadmap.md
- All gates approved: reviewer, security, qa; verify.sh green

project/src/shared/errors.ts

@@ -0,0 +1,15 @@
+/**
+ * Shared error envelope. Single shape for every API error.
+ * Never leak stack traces or internal details to the client.
+ */
+
+export interface ErrorEnvelope {
+  error: {
+    statusCode: number;
+    message: string;
+  };
+}
+
+export function errorEnvelope(statusCode: number, message: string): ErrorEnvelope {
+  return { error: { statusCode, message } };
+}