agent: Simplify design of the settings view (#29041)

Containing everything in boxes wasn't super necessary here. Want to
still improve the switch color contrast here, but will probably do that
in a separate PR.

<img
src="https://github.com/user-attachments/assets/f826a7a8-beaf-45d0-9dc2-36dc210c418e"
width="700"/>

Release Notes:

- N/A

crates/markdown/src/markdown.rs

@@ -753,11 +753,6 @@ impl Element for MarkdownElement {
                                             }
                                         });
 
-                                    // Apply border if required
-                                    // Usage examples:
-                                    // CodeBlockRenderer::Default { copy_button: true, border: true } - Both copy button and border
-                                    // CodeBlockRenderer::Default { copy_button: false, border: true } - Border only
-                                    // CodeBlockRenderer::Default { copy_button: true, border: false } - Copy button only (default)
                                     if let CodeBlockRenderer::Default { border: true, .. } =
                                         &self.code_block_renderer
                                     {