Add built-in theme support with various pre-defined themes

- Introduce multiple built-in themes (`default_dark`, `default_light`, `gruvbox`, `dracula`, `solarized`, `midnight-ocean`, `rose-pine`, `monokai`, `material-dark`, `material-light`).
- Implement theming system with customizable color schemes for all UI components in the TUI.
- Include documentation for themes in `themes/README.md`.
- Add fallback mechanisms for default themes in case of parsing errors.
- Support custom themes with overrides via configuration.

Cargo.toml

@@ -9,7 +9,7 @@ members = [
 exclude = []
 
 [workspace.package]
-version = "0.1.8"
+version = "0.1.9"
 edition = "2021"
 authors = ["Owlibou"]
 license = "AGPL-3.0"