refactor: Integrate Flyway for database migrations and simplify Docker Compose and tenant configurations.

backend/pom.xml

@@ -32,6 +32,12 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-data-jpa</artifactId>
         </dependency>
+        
+        <!-- Flyway Database Migrations -->
+        <dependency>
+            <groupId>org.flywaydb</groupId>
+            <artifactId>flyway-core</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.postgresql</groupId>
             <artifactId>postgresql</artifactId>