assistant2: Suggest recent files and threads as context (#22959)

The context picker will now display up to 6 recent files/threads to add
as a context:

<img
src="https://github.com/user-attachments/assets/80c87bf9-70ad-4e81-ba24-7a624378b991"
width=400>



Note: We decided to use a `ContextMenu` instead of `Picker` for the
initial one since the latter didn't quite fit the design for the
"Recent" section.

Release Notes:

- N/A

---------

Co-authored-by: Danilo <danilo@zed.dev>
Co-authored-by: Piotr <piotr@zed.dev>
Co-authored-by: Nathan <nathan@zed.dev>

crates/ui/src/utils/with_rem_size.rs

@@ -1,6 +1,7 @@
 use gpui::{
     div, AnyElement, Bounds, Div, DivFrameState, Element, ElementId, GlobalElementId, Hitbox,
-    IntoElement, LayoutId, ParentElement, Pixels, StyleRefinement, Styled, WindowContext,
+    InteractiveElement as _, IntoElement, LayoutId, ParentElement, Pixels, StyleRefinement, Styled,
+    WindowContext,
 };
 
 /// An element that sets a particular rem size for its children.
@@ -18,6 +19,13 @@ impl WithRemSize {
             rem_size: rem_size.into(),
         }
     }
+
+    /// Block the mouse from interacting with this element or any of its children
+    /// The fluent API equivalent to [`Interactivity::occlude_mouse`]
+    pub fn occlude(mut self) -> Self {
+        self.div = self.div.occlude();
+        self
+    }
 }
 
 impl Styled for WithRemSize {
@@ -37,7 +45,7 @@ impl Element for WithRemSize {
     type PrepaintState = Option<Hitbox>;
 
     fn id(&self) -> Option<ElementId> {
-        self.div.id()
+        Element::id(&self.div)
     }
 
     fn request_layout(