chore(validation): rework dto validation layer

[theEvilReaper]

Proposed changes

Recent commits removed the existing validation layer for DTOs. While this is acceptable for now, it’s not sustainable in the long run. This pull request introduces a new validation layer that works better for each case

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[Copilot]

Pull Request Overview

This PR adds Jakarta Bean Validation annotations to DTOs and implements comprehensive validation test coverage. The changes introduce field-level validation constraints (e.g., @NotBlank, @Positive, @PositiveOrZero) to ensure data integrity at the API layer.

• Added Jakarta Validation and Hibernate Validator dependencies
• Annotated DTO fields with validation constraints (@NotBlank, @NotEmpty, @Positive, @PositiveOrZero, @Nullable)
• Created a base validation test class and comprehensive validation tests for all DTOs
• Fixed field naming inconsistency (description → comment in NotificationModelDTO)

Reviewed Changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
settings.gradle.kts	Added version definitions for hibernate-validator (9.0.1.Final) and jakarta.validation-api (3.1.1)
build.gradle.kts	Added validation library dependencies to testImplementation and reordered testRuntimeOnly
ValidationTestBase.java	Created abstract base class with helper methods for validation testing using Jakarta Validator
SoundFileSourceDTO.java	Added validation constraints for name, volume, pitch, weight, attenuationDistance, and type fields
SoundEventDTO.java	Added @notblank and @NotNull constraints to uiName, variableName, keyName, and subTitle fields
NotificationModelDTO.java	Added validation constraints and renamed field from "description" to "comment"
ItemModelDTO.java	Added validation constraints for string fields and numeric fields (customModelData, amount)
FontModelDTO.java	Added validation constraints for string fields, marked comment as @nullable, added @PositiveOrZero for ascent/height
AttributeModelDTO.java	Added validation constraints for string fields and numeric constraints for defaultValue and maximumValue
SoundFileSourceDTOValidationTest.java	Created comprehensive tests validating blank/negative constraints on all fields
SoundEventDTOValidationTest.java	Created tests validating blank string constraints on all required fields
NotificationModelDTOValidationTest.java	Created tests validating blank string constraints on all required fields
ItemModelDTOValidationTest.java	Created tests validating blank strings, negative numbers, and comment nullability
FontModelDTOValidationTest.java	Created tests validating blank strings and negative numeric values
AttributeModelDTOValidationTest.java	Created tests validating empty strings and numeric constraints

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[TheMeinerLP]

LGTM