Timezone is now sent from the client on each request that needs it,
instead of storing it in the database. This simplifies the model and
allows timezone to be dynamic (useful for traveling users).
Changes:
- Remove timezone field from User entity
- Remove timezone from user registration
- GET /habits/today now requires ?timezone= query param
- Add migration to drop timezone column from database
- Update related tests
- Created i18n package with translator and middleware
- Added translation files for English (en.json) and Spanish (es.json)
- Updated all HTTP handlers to use i18n for error/success messages
- Added comprehensive test coverage for i18n (87%)
- Updated CI workflow to use Go 1.24
- All tests passing with 50.8% total coverage
david