feat(FN-3605): keep mobile header identity and toggle inline in ChatView

The merge completes Step 2 of FN-3605 by refactoring the ChatView mobile header to preserve its visual identity while converting the toggle control to an inline layout, accompanied by corresponding tests.

Fusion-Task-Id: FN-3605

packages/dashboard/app/components/ChatView.css

@@ -225,9 +225,17 @@
   gap: 8px;
 }
 
+.chat-thread-header-identity {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-sm);
+  min-width: 0;
+}
+
 .chat-thread-header-title {
   font-weight: 600;
   font-size: 15px;
+  min-width: 0;
 }
 
 .chat-thread-header-new-chat {
@@ -1100,7 +1108,24 @@
   }
 
   .chat-thread-header {
-    flex-wrap: wrap;
+    flex-wrap: nowrap;
+  }
+
+  .chat-thread-header-identity {
+    flex: 1 1 auto;
+    min-width: 0;
+    white-space: nowrap;
+    overflow: hidden;
+  }
+
+  .chat-thread-header-identity .chat-thread-header-title,
+  .chat-thread-header-identity .chat-model-tag {
+    overflow: hidden;
+    text-overflow: ellipsis;
+  }
+
+  .chat-thread-header-render-toggle {
+    flex-shrink: 0;
   }
 
   .chat-thread-header-new-chat {