[FEAT] Refactor API main file and models

This commit refactors the `main.go` file in the API directory, as well as the related models in the `models.go` file. The changes include:

- Reordering imports and removing unnecessary imports
- Fixing error messages to be more descriptive
- Handling database connections more efficiently with deferred closures
- Handling errors and returning appropriate error responses
- Adding proper JSON bindings for POST requests
- Adding new views in the database scripts for aggregated statistics and daily user statistics

No changes were made to imports and requires.

0 files changed, 0 insertions, 0 deletions