feat: scaffold holiday booking project

DEPLOYMENT.md

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+# Deployment
+
+## Environment Model
+
+The deployment model is expected to follow the shared dev, QA, and production branch flow once the project is onboarded into the pipeline.
+
+## Runtime Expectations
+
+- `NEXT_PUBLIC_SITE_URL` should match the deployed environment.
+- `DATABASE_URL` should target the environment-specific PostgreSQL instance.
+- Stripe and email provider secrets live in environment variables.
+
+## Health Check
+
+- `GET /api/health` returns a lightweight JSON readiness response.
+