v0.2.0 - Integration Testing Layer

Release v0.2.0

This release introduces the integration testing layer and improves HTTP error handling semantics.

Highlights:

• Added @WebMvcTest controller contract tests (MockMvc)
• Added @DataJpaTest repository tests (H2 in-memory DB)
• Fixed GlobalExceptionHandler to correctly return:
  • 400 for missing query parameters
  • 400 for enum/type mismatch
  • 400 for validation errors
  • 404 for NotFoundException
• Updated PROJECT_STATE.md milestone

All tests passing via Maven Wrapper.