Update module name and all imports from habit-tracker-api to apocapoc-api.
This reflects the project's new branding as part of the apocapoc ecosystem
(apocapoc-api, apocapoc-web, apocapoc-android).
- Add MIT License (Copyright 2025 David Folch Agulles)
- Add README with project description
- Add .gitignore for Go project
- Add .env.example for configuration
- Initialize Go module