fix(db): replace flyway-core with spring-boot-starter-flyway (#130)

Spring Boot 4.0 moved Flyway auto-configuration out of
spring-boot-autoconfigure into a dedicated starter module. Adding only
flyway-core to the classpath is no longer sufficient to trigger
FlywayAutoConfiguration or the spring.flyway.* properties — the starter
is required, following the same convention as spring-boot-starter-data-jpa,
spring-boot-starter-webmvc, etc.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nanotaboada

CHANGELOG.md

@@ -43,7 +43,9 @@ Release names follow the **historic football clubs** naming convention (A–Z):
 ### Added
 
 - Integrate Flyway for database schema versioning and automated migrations;
-  add `flyway-core` and `flyway-database-postgresql` to `pom.xml`; create
+  add `spring-boot-starter-flyway` (Spring Boot 4.0 requires this dedicated
+  starter for autoconfiguration — `flyway-core` alone is insufficient) and
+  `flyway-database-postgresql` to `pom.xml`; create
   migration directory `src/main/resources/db/migration/` with three versioned
   scripts: `V1__Create_players_table.sql` (schema), `V2__Seed_starting11.sql`
   (11 Starting XI players), `V3__Seed_substitutes.sql` (15 substitute players);

pom.xml

@@ -169,16 +169,18 @@
             <groupId>org.hibernate.orm</groupId>
             <artifactId>hibernate-community-dialects</artifactId>
         </dependency>
-        <!-- Flyway Core ================================================== -->
+        <!-- Spring Boot Starter Flyway ==================================== -->
         <!--
-            Flyway is an open-source database migration tool. It provides version
-            control for your database schema and automates migrations across all
-            environments. Includes built-in support for SQLite (community).
-            https://mvnrepository.com/artifact/org.flywaydb/flyway-core
+            Spring Boot 4.0 moved Flyway auto-configuration out of
+            spring-boot-autoconfigure into this dedicated starter. Adding only
+            flyway-core is no longer sufficient — this starter is required to
+            enable FlywayAutoConfiguration and the spring.flyway.* properties.
+            Transitively brings in flyway-core (version managed by Spring BOM).
+            https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-flyway
         -->
         <dependency>
-            <groupId>org.flywaydb</groupId>
-            <artifactId>flyway-core</artifactId>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-flyway</artifactId>
         </dependency>
         <!-- Flyway Database PostgreSQL ==================================== -->
         <!--