feat: add Todo API example project for Cloudflare Workers

Complete reference implementation demonstrating Nerva's Cloudflare Workers
deployment path with CRUD endpoints, D1 database, Zod validation, and
integration tests (15/15 passing).

- Hono REST API with middleware (CORS, security headers, request ID, ETag)
- Drizzle ORM with D1 (SQLite) schema and migration
- Zod request validation via @hono/zod-validator
- Vitest integration tests using Miniflare for real D1
- TypeScript strict mode with full Cloudflare Workers types
- README with setup, API docs, and deployment instructions
- Link added to main README Quick Start section

Closes #18

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Paul Mulligan

README.md

@@ -42,6 +42,8 @@ pnpm install
 cd api && pnpm dev
 ```
 
+> **New to Nerva?** See the [Todo API example](examples/todo-api-cloudflare/) for a complete working Cloudflare Workers project with CRUD, D1, Zod validation, and tests.
+
 ## Pipelines
 
 ### Schema-to-API (Autonomous)