assistant2: Adjust edit files design (#27762)

This PR includes design tweaks to elements involved on the "edit files"
flow: the bar that appears above the message editor, buttons on the
multibuffer hunks, adding keybindings to the "Review Changes" button,
etc.

<img
src="https://github.com/user-attachments/assets/4bff883a-c5c4-443e-8bf5-d98f535c83ce"
width="750" />

Release Notes:

- N/A

crates/assistant2/src/assistant_panel.rs

@@ -39,8 +39,8 @@ use crate::thread::{Thread, ThreadError, ThreadId};
 use crate::thread_history::{PastContext, PastThread, ThreadHistory};
 use crate::thread_store::ThreadStore;
 use crate::{
-    InlineAssistant, NewPromptEditor, NewThread, OpenActiveThreadAsMarkdown, OpenConfiguration,
-    OpenHistory,
+    AssistantDiff, InlineAssistant, NewPromptEditor, NewThread, OpenActiveThreadAsMarkdown,
+    OpenAssistantDiff, OpenConfiguration, OpenHistory,
 };
 
 action_with_deprecated_aliases!(
@@ -90,6 +90,14 @@ pub fn init(cx: &mut App) {
                         workspace.focus_panel::<AssistantPanel>(window, cx);
                         panel.update(cx, |panel, cx| panel.open_configuration(window, cx));
                     }
+                })
+                .register_action(|workspace, _: &OpenAssistantDiff, window, cx| {
+                    if let Some(panel) = workspace.panel::<AssistantPanel>(cx) {
+                        workspace.focus_panel::<AssistantPanel>(window, cx);
+                        panel.update(cx, |panel, cx| {
+                            panel.open_assistant_diff(&OpenAssistantDiff, window, cx);
+                        });
+                    }
                 });
         },
     )
@@ -432,6 +440,16 @@ impl AssistantPanel {
         })
     }
 
+    pub fn open_assistant_diff(
+        &mut self,
+        _: &OpenAssistantDiff,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        let thread = self.thread.read(cx).thread().clone();
+        AssistantDiff::deploy(thread, self.workspace.clone(), window, cx).log_err();
+    }
+
     pub(crate) fn open_configuration(&mut self, window: &mut Window, cx: &mut Context<Self>) {
         let context_server_manager = self.thread_store.read(cx).context_server_manager();
         let tools = self.thread_store.read(cx).tools();
@@ -1105,6 +1123,7 @@ impl Render for AssistantPanel {
             }))
             .on_action(cx.listener(Self::open_active_thread_as_markdown))
             .on_action(cx.listener(Self::deploy_prompt_library))
+            .on_action(cx.listener(Self::open_assistant_diff))
             .child(self.render_toolbar(window, cx))
             .map(|parent| match self.active_view {
                 ActiveView::Thread => parent