Task 10 feat: dockerize application, add Swagger docs and global exce…

[dawiddykacz]

Description

This PR introduces full containerization, interactive API documentation, and standardizes error handling across the application. It also resolves dependency conflicts and adds a comprehensive README for easier onboarding.

Key Changes

Dockerization: Added a multi-stage Dockerfile and docker-compose.yml for seamless local development without requiring local Java/Maven setups.
Swagger UI: Integrated springdoc-openapi (v2.6.0). Configured Spring Security to expose /swagger-ui/** and /v3/api-docs endpoints. Added descriptive annotations to AuthController and DTOs.
Global Exception Handling: Implemented @RestControllerAdvice. Created a custom UserAlreadyExistsException mapped to 409 Conflict (replacing the previous null-return logic).

• Removed invalid webmvc starter references.
  Database Config: Changed spring.jpa.hibernate.ddl-auto to update to prevent dropping tables on container restarts
  Documentation: Added a detailed README.md with tech stack, setup instructions, and Swagger guidelines.

How to test

1. Run docker-compose up --build -d
2. Navigate to http://localhost:8082/swagger-ui.html
3. Try registering a user.
4. Try registering the same user again to verify the 409 Conflict response.