Adds spring-boot-testcontainers and testcontainers-postgresql deps.
PostgresContainerConfig declares a shared @ServiceConnection container
used by DocumentRepositoryTest, PersonRepositoryTest, and an
ApplicationContextTest smoke test.
Flyway migrations are imported via FlywayConfig and run on every test
execution, verifying the migration chain against a real PostgreSQL 16
container. No H2 is used.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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