assistant2: Adjust empty state layout (#25745)

Going for a different, arguably simpler design for the Assistant 2 empty
state here. Also took the opportunity to adjust other elements like the
toolbar, message editor, and some items in the configuration page.

<img
src="https://github.com/user-attachments/assets/03fd1d48-a675-4eac-b694-bbe4eeaf06e9"
width="700px"/>

Release Notes:

- N/A

crates/language_models/src/provider/cloud.rs

@@ -386,17 +386,10 @@ fn render_accept_terms(
     let form = v_flex()
         .w_full()
         .gap_2()
-        .when(
-            view_kind == LanguageModelProviderTosView::ThreadEmptyState,
-            |form| form.items_center(),
-        )
         .child(
             h_flex()
                 .flex_wrap()
-                .when(
-                    view_kind == LanguageModelProviderTosView::ThreadEmptyState,
-                    |form| form.justify_center(),
-                )
+                .items_start()
                 .child(Label::new(text))
                 .child(terms_button),
         )
@@ -416,9 +409,11 @@ fn render_accept_terms(
             );
 
             match view_kind {
-                LanguageModelProviderTosView::ThreadEmptyState => button_container.justify_center(),
                 LanguageModelProviderTosView::PromptEditorPopup => button_container.justify_end(),
-                LanguageModelProviderTosView::Configuration => button_container.justify_start(),
+                LanguageModelProviderTosView::Configuration
+                | LanguageModelProviderTosView::ThreadEmptyState => {
+                    button_container.justify_start()
+                }
             }
         });