fix(api): add spring-boot-starter-flyway for Spring Boot 4 migrations

Backend crashed on startup with 'Schema validation: missing table
[audit_events]'. Root cause: this is Spring Boot 4.0.6, which modularized
autoconfiguration. FlywayAutoConfiguration moved out of spring-boot-autoconfigure
into a dedicated spring-boot-flyway module that is only pulled in by
spring-boot-starter-flyway. The pom only had flyway-database-postgresql
(+ transitive flyway-core) but NOT the starter, so spring.flyway.enabled=true
was inert: no migrations ran, flyway_schema_history was never created, and
Hibernate ddl-auto=validate failed on the empty schema.

Adds spring-boot-starter-flyway (autoconfigure module + flyway-core); keeps
flyway-database-postgresql for the Postgres dialect.
Ref: https://spring.io/blog/2025/10/28/modularizing-spring-boot/

cannamanage-api/pom.xml

@@ -36,6 +36,18 @@
             <artifactId>postgresql</artifactId>
             <scope>runtime</scope>
         </dependency>
+        <!--
+          Spring Boot 4 modularized autoconfiguration: FlywayAutoConfiguration
+          moved out of spring-boot-autoconfigure into the dedicated spring-boot-flyway
+          module, which is only brought in by spring-boot-starter-flyway. Without this
+          starter, spring.flyway.enabled=true is inert — migrations never run and
+          Hibernate ddl-auto=validate fails on the empty schema.
+          See: https://spring.io/blog/2025/10/28/modularizing-spring-boot/
+        -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-flyway</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.flywaydb</groupId>
             <artifactId>flyway-database-postgresql</artifactId>