fix: 手机版emoji按钮加圆角边框，与视图切换按钮风格一致

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/OilReference.vue

@@ -1265,11 +1265,16 @@ async function saveCardImage(name) {
 .toolbar-btn-text:hover { background: var(--sage-mist); }
 .toolbar-btn-icon {
   display: none;
-  background: none;
-  border: none;
-  font-size: 18px;
+  background: white;
+  border: 1.5px solid var(--border);
+  border-radius: 10px;
+  font-size: 16px;
   cursor: pointer;
-  padding: 4px;
+  padding: 6px 10px;
+}
+.toolbar-btn-icon:hover {
+  border-color: var(--sage);
+  background: var(--sage-mist);
 }
 
 @media (max-width: 480px) {