fix(FN-2906): refine chat render toggles and quick chat resume state

- Remove btn-icon styling from ChatView render toggle controls and apply dedicated borderless toggle styling
- Update ChatView and QuickChatFAB behavior so quick chat streaming state is preserved when resuming sessions
- Add regression tests for QuickChatFAB and useQuickChat to cover resume and streaming-state handling

Fusion-Task-Id: FN-2906

packages/dashboard/app/components/ChatView.css

@@ -231,15 +231,19 @@
 
 .chat-message-render-toggle {
   display: inline-flex;
+  align-items: center;
+  justify-content: center;
   margin-left: auto;
   width: calc(var(--space-md) * 3);
   height: calc(var(--space-md) * 3);
   min-width: calc(var(--space-md) * 3);
   min-height: calc(var(--space-md) * 3);
   padding: 0;
+  border: none;
   color: var(--text-muted);
   background: transparent;
-  border-color: transparent;
+  cursor: pointer;
+  outline: none;
 }
 
 .chat-message--assistant .chat-message-render-toggle {

packages/dashboard/app/components/ChatView.tsx

@@ -1276,7 +1276,7 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
                         {showAssistantModelTag && <span className="chat-model-tag">{activeModelTag}</span>}
                         <button
                           type="button"
-                          className={`btn btn-icon chat-message-render-toggle${forcePlain ? " chat-message-render-toggle--plain" : ""}`}
+                          className={`chat-message-render-toggle${forcePlain ? " chat-message-render-toggle--plain" : ""}`}
                           data-testid="chat-message-render-toggle"
                           aria-label={forcePlain ? "Show rendered markdown" : "Show plain text"}
                           onClick={() => toggleMessageRenderMode(message.id)}
@@ -1307,7 +1307,7 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
                     {showAssistantModelTag && <span className="chat-model-tag">{activeModelTag}</span>}
                     <button
                       type="button"
-                      className={`btn btn-icon chat-message-render-toggle${plainTextMessageIds.has("__streaming__") ? " chat-message-render-toggle--plain" : ""}`}
+                      className={`chat-message-render-toggle${plainTextMessageIds.has("__streaming__") ? " chat-message-render-toggle--plain" : ""}`}
                       data-testid="chat-message-render-toggle"
                       aria-label={plainTextMessageIds.has("__streaming__") ? "Show rendered markdown" : "Show plain text"}
                       onClick={() => toggleMessageRenderMode("__streaming__")}