agent: Refresh the profile selector and modal design (#29816)

- [x] Separate MCP servers from tools in the profile customization modal
view
- [x] Group MCP tools in the MCP picker and add a heading
- [x] Separate bult-in profiles from custom ones in the dropdown
selector
- [x] Separate bult-in profiles from custom ones in the modal
- [ ] Enable looping through items via keybinding without opening the
dropdown (will be done on a follow-up PR)
- [ ] Stretch: Focus on the currently active item upon opening the
dropdown (will be done on a follow-up PR)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <53836821+bennetbo@users.noreply.github.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>

crates/ui/src/components/navigable.rs

@@ -19,14 +19,14 @@ pub struct NavigableEntry {
 
 impl NavigableEntry {
     /// Creates a new [NavigableEntry] for a given scroll handle.
-    pub fn new(scroll_handle: &ScrollHandle, cx: &mut App) -> Self {
+    pub fn new(scroll_handle: &ScrollHandle, cx: &App) -> Self {
         Self {
             focus_handle: cx.focus_handle(),
             scroll_anchor: Some(ScrollAnchor::for_handle(scroll_handle.clone())),
         }
     }
     /// Create a new [NavigableEntry] that cannot be scrolled to.
-    pub fn focusable(cx: &mut App) -> Self {
+    pub fn focusable(cx: &App) -> Self {
         Self {
             focus_handle: cx.focus_handle(),
             scroll_anchor: None,