feat: Redis/MySQL 加载骨架屏 loading 效果

- SchemaSidebar: MySQL 表列表加载改为 6 行骨架屏 animate-pulse
- SchemaSidebar: Redis key 列表加载改为 6 行骨架屏 animate-pulse
- RedisDetailPage: key 表格加载时显示 5 行骨架屏 + 加载中提示
- 替换原来的纯文字/spinner，视觉上更流畅

frontend/src/pages/RedisDetailPage.tsx

@@ -137,6 +137,21 @@ export default function RedisDetailPage() {
 
           {/* 键列表 */}
           <div className="overflow-x-auto">
+            {loading ? (
+              <div className="space-y-2 p-4">
+                {Array.from({ length: 5 }, function (_, i) {
+                  return <div key={i} className="flex items-center gap-4">
+                    <div className="h-4 bg-[var(--dg-bg-tertiary)] rounded animate-pulse flex-1" />
+                    <div className="h-4 bg-[var(--dg-bg-tertiary)] rounded animate-pulse w-16" />
+                    <div className="h-4 bg-[var(--dg-bg-tertiary)] rounded animate-pulse w-12" />
+                    <div className="h-4 bg-[var(--dg-bg-tertiary)] rounded animate-pulse w-20" />
+                  </div>;
+                })}
+                <div className="text-center text-xs text-[var(--dg-text-muted)] pt-2">加载中...</div>
+              </div>
+            ) : keys.length === 0 ? (
+              <div className="text-center py-8 text-[var(--dg-text-muted)]">点击刷新加载键列表</div>
+            ) : (
             <table className="w-full text-sm">
               <thead><tr className="text-left text-[var(--dg-text-muted)] border-b border-[var(--dg-border)]">
                 <th className="px-4 py-2">键名</th><th className="px-4 py-2">类型</th><th className="px-4 py-2">TTL</th><th className="px-4 py-2">操作</th>
@@ -157,7 +172,7 @@ export default function RedisDetailPage() {
                 })}
               </tbody>
             </table>
-            {keys.length === 0 && <div className="text-center py-8 text-[var(--dg-text-muted)]">点击刷新加载键列表</div>}
+            )}
           </div>
         </div>
       )}