feat(ui): add solid background color option for input prompt (#16563)

Co-authored-by: Alexander Farber <farber72@outlook.de>

docs/get-started/configuration.md

@@ -244,16 +244,16 @@ their corresponding top-level category object in your `settings.json` file.
   - **Description:** Show the model name in the chat for each model turn.
   - **Default:** `false`
 
-- **`ui.useFullWidth`** (boolean):
-  - **Description:** Use the entire width of the terminal for output.
-  - **Default:** `true`
-
 - **`ui.useAlternateBuffer`** (boolean):
   - **Description:** Use an alternate screen buffer for the UI, preserving shell
     history.
   - **Default:** `false`
   - **Requires restart:** Yes
 
+- **`ui.useBackgroundColor`** (boolean):
+  - **Description:** Whether to use background colors in the UI.
+  - **Default:** `true`
+
 - **`ui.incrementalRendering`** (boolean):
   - **Description:** Enable incremental rendering for the UI. This option will
     reduce flickering but may cause rendering artifacts. Only supported when