feat: scaffold holiday booking project

ARCHITECTURE.md

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+# Architecture
+
+## Initial Shape
+
+- `src/app` contains route-level UI and the health endpoint.
+- `src/components` contains reusable layout pieces.
+- `src/lib` contains shared data and infrastructure helpers.
+- `prisma/` contains the initial database schema and seed entrypoint.
+
+## Notes
+
+- The UI starts as server-rendered pages with a small client-free shell.
+- Database access will flow through Prisma once the app starts reading real records.
+- Feature work should keep the booking state model and payment state model separate.
+