Show prompt usage in agent overflow menu (#29922)

This PR adds prompt usage information, and easy access to managing your
account, to the agent overflow menu:

![CleanShot 2025-05-05 at 10 04
20@2x](https://github.com/user-attachments/assets/337a1a0b-6f71-49a0-9fe7-4fbf2ec1fc27)

Currently this UI will only show after making a request. We'll work on
eagerly getting the usage info later.

Release Notes:

- Added current prompt usage information to the agent menu (`...`) for
Zed AI users

crates/ui/src/components/context_menu.rs

@@ -16,6 +16,8 @@ use super::Tooltip;
 pub enum ContextMenuItem {
     Separator,
     Header(SharedString),
+    /// title, link_label, link_url
+    HeaderWithLink(SharedString, SharedString, SharedString), // This could be folded into header
     Label(SharedString),
     Entry(ContextMenuEntry),
     CustomEntry {
@@ -332,6 +334,20 @@ impl ContextMenu {
         self
     }
 
+    pub fn header_with_link(
+        mut self,
+        title: impl Into<SharedString>,
+        link_label: impl Into<SharedString>,
+        link_url: impl Into<SharedString>,
+    ) -> Self {
+        self.items.push(ContextMenuItem::HeaderWithLink(
+            title.into(),
+            link_label.into(),
+            link_url.into(),
+        ));
+        self
+    }
+
     pub fn separator(mut self) -> Self {
         self.items.push(ContextMenuItem::Separator);
         self
@@ -788,6 +804,25 @@ impl ContextMenu {
             ContextMenuItem::Header(header) => ListSubHeader::new(header.clone())
                 .inset(true)
                 .into_any_element(),
+            ContextMenuItem::HeaderWithLink(header, label, url) => {
+                let url = url.clone();
+                let link_id = ElementId::Name(format!("link-{}", url).into());
+                ListSubHeader::new(header.clone())
+                    .inset(true)
+                    .end_slot(
+                        Button::new(link_id, label.clone())
+                            .color(Color::Muted)
+                            .label_size(LabelSize::Small)
+                            .size(ButtonSize::None)
+                            .style(ButtonStyle::Transparent)
+                            .on_click(move |_, _, cx| {
+                                let url = url.clone();
+                                cx.open_url(&url);
+                            })
+                            .into_any_element(),
+                    )
+                    .into_any_element()
+            }
             ContextMenuItem::Label(label) => ListItem::new(ix)
                 .inset(true)
                 .disabled(true)
@@ -1057,6 +1092,7 @@ impl ContextMenuItem {
     fn is_selectable(&self) -> bool {
         match self {
             ContextMenuItem::Header(_)
+            | ContextMenuItem::HeaderWithLink(_, _, _)
             | ContextMenuItem::Separator
             | ContextMenuItem::Label { .. } => false,
             ContextMenuItem::Entry(ContextMenuEntry { disabled, .. }) => !disabled,