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/README.md

@@ -0,0 +1,38 @@
+# MercadoDeVida backend — modular monolith skeleton
+
+TypeScript + Fastify modular monolith. Simple code, clear modules, small changes, no magic.
+
+## Requirements
+
+- Node.js >= 22
+- npm
+
+## Commands
+
+```bash
+npm install           # install dependencies
+npm run build         # compile to dist/
+npm start             # run compiled server (PORT, HOST env vars)
+npm test              # vitest unit/integration tests
+npm run typecheck     # tsc --noEmit
+npm run lint          # eslint + prettier check
+npm run lint:boundaries  # module boundary check
+```
+
+## Layout
+
+```text
+src/
+├── app/             # composition root (only place that wires modules)
+├── infrastructure/  # http server entrypoint (later: db, redis, providers)
+├── modules/         # business modules, one folder each
+│   └── health/      # exemplar module: public API only via index.ts
+└── shared/          # cross-cutting helpers (error envelope)
+```
+
+## Module rules
+
+- A module exposes its public API only through its `index.ts`.
+- Files inside a module may import: own subtree, `src/shared`, Node builtins, npm packages.
+- Code outside modules (app/infrastructure) may import a module only via its `index.ts`.
+- `npm run lint:boundaries` enforces these rules.