OrderHub Day 2: Persisting Orders with JPA + PostgreSQL (Spring Boot)

OrderHub Day 1 stored orders in a HashMap — restart the server and they're gone. Day 2 fixes that: real persistence with JPA + PostgreSQL, and thanks to Day 1's layered design, the controller and service don't change a single line.

🗄️ See it (place orders, "restart", watch what survives):

OrderHub — a production-grade Spring Boot backend, one feature a day.

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