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.

This commit adds functionality to add water statistics to the DataView component. It includes the following changes:
- Remove unused imports and variables
- Move the 'handleClick' function logic to a new 'AddForm' component
- Create the 'AddForm' component which displays a dialog with input fields for date and quantity and allows the user to add a new water statistic
- Dispatch events on form submit and dialog close in the 'AddForm' component
- Call the 'fetchData' function on successful submission of a new statistic
- Update chart data to display sample data

New component:
- AddForm.svelte: A form component to add a new water statistic

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