'Get Theme' endpoint and Theme loading on Backend

[MrVintage710]

Proposed Feature

Add the ability for the backend to automatically load in json files that are stored near the app, and make an endpoint for the front end to get a list of themes.

There are dummy versions of these endpoints as well as the VitruvianTheme type are being added with PR #31. I would recommend waiting for that PR to land, then starting this ticket.

Acceptance Criteria

• Make sure all features are well documented with JSDoc. Here is a guide for more info.
• Add all commands to the following file : /src-tauri/src/commands/themes.rs
• Add the following tauri commands
  • get_current_theme() -> VitruvianTheme gets the current theme selected by the user. If not set, should default to the red theme.
  • set_current_theme(theme : VitruvianTheme) should set the theme and persist it between loads
  • get_available_themes() -> Vec<String> Returns a list of theme names that are available for the frontend to use.
  • get_theme(theme_id : String) -> VitruvianTheme Returns a specific theme based on the theme ID