[Feature Request]: Remove leftover `btn-` classes and replace with `md-`

### Preflight Checklist

- [x] I have read the [Contributing Guidelines](https://github.com/EnAccess/micropowermanager/blob/main/CONTRIBUTING.md) for this project, if it exists.
- [x] I agree to follow the [Code of Conduct](https://github.com/EnAccess/micropowermanager/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [x] I have searched the [issue tracker](https://github.com/EnAccess/micropowermanager/issues) for a feature request that matches the one I want to file, without success.

### Problem Description

In the frontend code there is mixture between `md-` classes and `btn-` classes for buttons. As a result some buttons look off

### Proposed Solution

Please replace all `btn-` classes with their Vue Material equivalents.

Should look like this

### Alternatives Considered

N/A

### Additional Information

_No response_

Start by searching the frontend code for all `btn-` and `md-` class usages, then inspect how the Vue Material button classes are applied. Done means no leftover `btn-` classes remain and the affected buttons match the expected Vue Material appearance shown in the issue.

Written by the indexing model from the issue text.