chore: configure CodeRabbit for Java 25/Spring Boot 4 project

- Add comprehensive path-based review instructions for Java/Spring Boot
  architecture layers (controllers, services, repositories, models), test
  patterns, and infrastructure files
- Configure relevant tools (PMD, Gitleaks, Checkov, Hadolint) while
  disabling language-specific tools not applicable to Java projects
- Set project-specific filters, coverage threshold (80%), and enforce
  Conventional Commits format for PR titles

Author: nanotaboada