Implement auth domain with outside-in TDD (22 tests)

Controller (7 tests): signup, login, logout, GET/PATCH me.
Standalone MockMvc setup (Boot 4 removed @WebMvcTest).

Service (11 tests): signup with conflict check, login with
password/active validation, getCurrentUser with household info,
updateProfile with password change flow.

Repository (4 tests): save/find, case-insensitive email via
IgnoreCase queries (citext + Hibernate needs explicit IgnoreCase),
existsByEmail.

Also includes:
- SecurityConfig: session auth, CSRF, role-based authorization
- CustomUserDetailsService: loads UserAccount for Spring Security
- UserAccount, Household, HouseholdMember JPA entities
- spring-boot-flyway dependency (Boot 4 requires explicit module)
- ddl-auto=none (Flyway owns schema, validate fails on citext)

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

backend/pom.xml

@@ -36,8 +36,8 @@
 			<artifactId>spring-boot-starter-web</artifactId>
 		</dependency>
 		<dependency>
-			<groupId>org.flywaydb</groupId>
-			<artifactId>flyway-core</artifactId>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-flyway</artifactId>
 		</dependency>
 		<dependency>
 			<groupId>org.flywaydb</groupId>
@@ -67,13 +67,13 @@
 		</dependency>
 		<dependency>
 			<groupId>org.testcontainers</groupId>
-			<artifactId>junit-jupiter</artifactId>
+			<artifactId>testcontainers</artifactId>
 			<version>${testcontainers.version}</version>
 			<scope>test</scope>
 		</dependency>
 		<dependency>
 			<groupId>org.testcontainers</groupId>
-			<artifactId>postgresql</artifactId>
+			<artifactId>testcontainers-postgresql</artifactId>
 			<version>${testcontainers.version}</version>
 			<scope>test</scope>
 		</dependency>