4.0.0-M1

The 4.x line is the long-term track that will move commons-rest onto Spring Boot 4 and eventually Jackson 3. We're currently waiting on Swagger/OpenAPI tooling to ship Jackson 3 compatibility
before we can complete that jump — until then, 4.x milestones stabilize on the current Spring Boot 3.5 / Jackson 2 baseline.

This milestone is a cleanup and optimization pass on the OpenAPI generator (commons-rest-openapi):

• Refactored the standalone TypeScript client generator
• Replaced string-based type conversion with typescript-generator for more reliable Java → TypeScript mapping
• Added Zod schema generation with improved nullable handling
• Updated React Query integration to v5, with corrected abort-signal handling
• Added enumValue support and a migration guide with deprecation warnings
• Dropped MapStruct in favor of the shared common validator
• Removed the PostHog integration
• Simplified TokenService and various utility helpers
• Dependency bumps (Spring Boot 3.5.14, Springdoc 2.8.15)