assistant: Improve discoverability of terminal inline assist (#15431)

This adds a button to the terminal tab bar:

<img width="444" alt="image"
src="https://github.com/user-attachments/assets/71baadae-0ecf-493f-853c-34d4d6a48310">


Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -94,6 +94,31 @@ pub fn init(cx: &mut AppContext) {
         },
     )
     .detach();
+
+    cx.observe_new_views(
+        |terminal_panel: &mut TerminalPanel, cx: &mut ViewContext<TerminalPanel>| {
+            let settings = AssistantSettings::get_global(cx);
+            if !settings.enabled {
+                return;
+            }
+
+            terminal_panel.register_tab_bar_button(cx.new_view(|_| InlineAssistTabBarButton), cx);
+        },
+    )
+    .detach();
+}
+
+struct InlineAssistTabBarButton;
+
+impl Render for InlineAssistTabBarButton {
+    fn render(&mut self, cx: &mut ViewContext<Self>) -> impl IntoElement {
+        IconButton::new("terminal_inline_assistant", IconName::MagicWand)
+            .icon_size(IconSize::Small)
+            .on_click(cx.listener(|_, _, cx| {
+                cx.dispatch_action(InlineAssist::default().boxed_clone());
+            }))
+            .tooltip(move |cx| Tooltip::for_action("Inline Assist", &InlineAssist::default(), cx))
+    }
 }
 
 pub enum AssistantPanelEvent {