refactor(core): Unify components and adopt standard tooling

This commit performs several key refactorings within the `core`-module to improve consistency, stability, and adhere to industry best practices.

1.  **Unify `Result` Type:**
    Removed the specialized `Result<T>` class from `core-utils`. The entire system will now exclusively use the more flexible and type-safe `Result<T, E>` from `core-domain`. This allows for explicit, non-exception-based error handling for business logic.

2.  **Adopt Flyway for Database Migrations:**
    Replaced the custom `DatabaseMigrator.kt` implementation with the industry-standard tool Flyway. The `DatabaseFactory` now triggers Flyway migrations on application startup. This provides more robust, transactional, and feature-rich schema management.

3.  **Cleanup and Housekeeping:**
    - Removed obsolete test files related to the old migrator.
    - Ensured all components align with the new unified patterns.

BREAKING CHANGE: The `at.mocode.core.utils.error.Result` class has been removed. All modules must be updated to use the `at.mocode.core.domain.error.Result` type. The custom migrator is no longer available.

Closes #ISSUE_NUMBER_FOR_REFACTORING

masterdata/masterdata-application/src/main/kotlin/at/mocode/masterdata/application/usecase/CreateAltersklasseUseCase.kt

@@ -215,7 +215,7 @@ class CreateAltersklasseUseCase(
 
         // Age class code validation
         if (request.altersklasseCode.isBlank()) {
-            errors.add(ValidationError("altersklasseCode", "Age class code is required", "REQUIRED"))
+            errors.add(ValidationError("altersklasseCode", "Age class code is required", "REQUIRED")) // "REQUIRED"
         } else if (request.altersklasseCode.length > 50) {
             errors.add(ValidationError("altersklasseCode", "Age class code must not exceed 50 characters", "MAX_LENGTH"))
         } else if (!request.altersklasseCode.matches(Regex("^[A-Z0-9_]+$"))) {