refactor: 将情景图标和设备选择器的 emoji 统一替换为 SVG 图标

- 新增 scenarioIcons.tsx 提取情景图标渲染逻辑
- 情景芯片、设备选择器、警告提示等 emoji 全部改为 Feather-style SVG
- 调整 CSS 确保 SVG 图标居中对齐

frontend/src/App.css

@@ -1623,15 +1623,17 @@ body {
 }
 
 .scenario-chip--add .scenario-chip__icon {
-  font-size: 0.88rem;
-  font-weight: 300;
-  line-height: 1;
+  display: inline-flex;
+  align-items: center;
 }
 
 .scenario-chip__icon {
   font-size: 0.9rem;
   line-height: 1;
   flex-shrink: 0;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
 }
 
 .scenario-chip__name {
@@ -1681,6 +1683,9 @@ body {
   font-size: 0.72rem;
   color: var(--color-text-muted);
   flex-shrink: 0;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
 }
 
 .device-select {