fix(FN-2646): restore quick chat render toggle visibility

- Remove generic btn btn-icon classes from quick chat render toggles so component-specific visibility styles apply
- Increase toggle icon size and adjust default muted color for clearer eye/eye-off affordance in assistant messages
- Add explicit focus-visible ring styling for keyboard accessibility on the render toggle control
- Extend QuickChatFAB regression coverage to assert class usage, SVG icon presence, and plain/rendered toggle state transitions

packages/dashboard/app/components/QuickChatFAB.css

@@ -293,11 +293,12 @@
   justify-content: center;
   opacity: 0;
   transition: opacity var(--transition-fast);
-  color: var(--text-tertiary);
+  color: var(--text-muted);
   background: transparent;
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
+  outline: none;
 }
 
 .quick-chat-panel-message--received:hover .quick-chat-message-render-toggle,
@@ -315,6 +316,11 @@
   color: var(--text);
 }
 
+.quick-chat-message-render-toggle:focus-visible {
+  outline: none;
+  box-shadow: var(--focus-ring-strong);
+}
+
 .quick-chat-panel-input {
   display: flex;
   align-items: center;