This commit introduces the `User` and `Expense` data classes as Room entities. Each entity is accompanied by its corresponding Data Access Object (DAO) with methods for `getAll`, `insert`, and `delete` operations.
Additionally, unused comments were removed from `MainViewModel` and an unnecessary preview was removed from `MainActivity`.
The login process has been expanded to include fields for Server URL, Username, and Password, replacing the previous User ID-only login.
The UI now utilizes `navigationBarsPadding` to prevent overlap with system navigation elements on the Login, Account Selection, and generic screens. The `Account` entity has been updated to include a `serverUrl`.
