agent: Support vim-mode in the agent panel's editor (#31915)

Closes #30081

Release Notes:

- Added vim-mode support in the agent panel's editor

---------

Co-authored-by: Ben Kunkle <ben.kunkle@gmail.com>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/vim/src/vim.rs

@@ -433,6 +433,12 @@ impl Vim {
     fn activate(editor: &mut Editor, window: &mut Window, cx: &mut Context<Editor>) {
         let vim = Vim::new(window, cx);
 
+        if !editor.mode().is_full() {
+            vim.update(cx, |vim, _| {
+                vim.mode = Mode::Insert;
+            });
+        }
+
         editor.register_addon(VimAddon {
             entity: vim.clone(),
         });