agent: Make terminal command render with Markdown in the tool card (#30430)

Closes https://github.com/zed-industries/zed/issues/30411

Rendering as markdown gives us text selection and copying for free. In
the future, we may want to explore having these commands be actual
editors, allowing you to step in, change the command, and re-run it
right from there.

Release Notes:

- agent: Made the terminal command in the tool card selectable and
copyable.

crates/assistant_tools/src/edit_file_tool.rs

@@ -637,7 +637,7 @@ impl ToolCard for EditFileToolCard {
                 .p_3()
                 .gap_1()
                 .border_t_1()
-                .rounded_md()
+                .rounded_b_md()
                 .border_color(border_color)
                 .bg(cx.theme().colors().editor_background);