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-local.properties.example

@@ -0,0 +1,6 @@
+# Local development database
+# Copy this file to application-local.properties and adjust as needed.
+# Start with: ./mvnw spring-boot:run -Dspring-boot.run.profiles=local
+spring.datasource.url=jdbc:postgresql://localhost:5432/fete
+spring.datasource.username=fete
+spring.datasource.password=fete

backend/src/main/resources/application-prod.properties

@@ -0,0 +1,4 @@
+# Database (required)
+spring.datasource.url=${DATABASE_URL}
+spring.datasource.username=${DATABASE_USERNAME}
+spring.datasource.password=${DATABASE_PASSWORD}

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

backend/src/main/resources/db/changelog/000-baseline.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <changeSet id="000-baseline" author="nitrix">
+        <comment>Baseline changeset — Liquibase tooling verification</comment>
+    </changeSet>
+
+</databaseChangeLog>

backend/src/main/resources/db/changelog/db.changelog-master.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <include file="db/changelog/000-baseline.xml"/>
+
+</databaseChangeLog>