v0.6.0 — API Contract Stabilization

v0.6.0 — Stable API Contracts & Pagination Standardization

Highlights:

• Introduced PageResponse pagination envelope to decouple API responses from Spring PageImpl
• Standardized error responses with ApiError and ValidationError DTOs
• GlobalExceptionHandler now returns typed error contracts including request path
• Added Pageable-based listOrders(Pageable) service method
• Updated WebMvc controller tests to validate new pagination response structure
• Improved API consistency for validation, parameter, and type mismatch errors

This release stabilizes the external API contract and prepares the service for future client integrations.