T-4: add JPA, Liquibase, Testcontainers, and deployment docs

Set up development infrastructure for TDD: JPA + Liquibase for
database migrations, Testcontainers for integration tests against
real PostgreSQL, profile-based configuration (prod/local), and
README deployment documentation with docker-compose example.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/resources/application.properties

@@ -1,4 +1,12 @@
 spring.application.name=fete
 
+# JPA
+spring.jpa.hibernate.ddl-auto=validate
+spring.jpa.open-in-view=false
+
+# Liquibase
+spring.liquibase.change-log=classpath:db/changelog/db.changelog-master.xml
+
+# Actuator
 management.endpoints.web.exposure.include=health
 management.endpoint.health.show-details=never