Gruvbox Light Theme

Given one or two themes that are well known and already ported to gitui, we can use AI to generate other well known themes.

This is an example of using Gemini 2.5 to port the Catppuccin theme to Gruvbox Light:

```ron
(
selected_tab: Some("Reset"),
command_fg: Some("#3c3836"), // fg (Main Text)
selection_bg: Some("#ebdbb2"), // bright_bg (Selection/Accent Background)
selection_fg: Some("#3c3836"), // fg (Text on selection)
cmdbar_bg: Some("#ebdbb2"), // bright_bg
cmdbar_extra_lines_bg: Some("#ebdbb2"), // bright_bg
disabled_fg: Some("#928374"), // gray (Secondary/Faded text)
diff_line_add: Some("#98971a"), // green
diff_line_delete: Some("#cc241d"), // red
diff_file_added: Some("#98971a"), // green
diff_file_removed: Some("#cc241d"), // red
diff_file_moved: Some("#b16286"), // purple
diff_file_modified: Some("#d79921"), // yellow
commit_hash: Some("#458588"), // blue (Link/identifier color)
commit_time: Some("#928374"), // gray (Secondary text)
commit_author: Some("#689d6a"), // aqua
danger_fg: Some("#cc241d"), // red (Error/Danger)
push_gauge_bg: Some("#458588"), // blue (Accent color for the gauge bar)
push_gauge_fg: Some("#fbf1c7"), // bg (The lightest color for text inside the blue gauge)
tag_fg: Some("#d65d0e"), // orange
branch_fg: Some("#458588") // blue
)

```

Is this an acceptable way to create themes and perhaps add them to gitui with an easy way to select a theme at runtime, and save that preference?

Non vengono indicati file, test o punti di ingresso. Inizia individuando le definizioni dei temi esistenti di gitui e qualsiasi configurazione attuale per la selezione dei temi; il lavoro sarà completato quando sarà stato deciso un approccio per aggiungere Gruvbox Light, selezionare i temi a runtime e salvare questa preferenza.

Scritto dal modello di indicizzazione a partire dal testo della issue.