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/components/SchemaSidebar.tsx

@@ -215,8 +215,14 @@ export default function SchemaSidebar({ instanceId, database, dbType, onInsert }
             {/* Table List */}
             <div className="flex-1 overflow-y-auto">
               {loadingTables ? (
-                <div className="flex items-center gap-2 p-3 text-xs text-[var(--dg-text-muted)]">
-                  <Loader2 className="w-3 h-3 animate-spin" /> 加载中...
+                <div className="space-y-1 p-2">
+                  {Array.from({ length: 6 }, (_, i) => (
+                    <div key={i} className="flex items-center gap-2 px-2 py-1.5">
+                      <div className="w-3 h-3 bg-[var(--dg-bg-tertiary)] rounded animate-pulse" />
+                      <div className="h-3.5 bg-[var(--dg-bg-tertiary)] rounded animate-pulse flex-1" />
+                      <div className="h-3 bg-[var(--dg-bg-tertiary)] rounded animate-pulse w-8" />
+                    </div>
+                  ))}
                 </div>
               ) : filteredTables.length === 0 ? (
                 <div className="p-3 text-xs text-[var(--dg-text-muted)] text-center">无表</div>
@@ -311,10 +317,18 @@ export default function SchemaSidebar({ instanceId, database, dbType, onInsert }
 
             {/* Key List + Detail */}
             <div className="flex-1 overflow-y-auto">
-              {redisKeys.length === 0 ? (
-                <div className="p-3 text-xs text-[var(--dg-text-muted)] text-center">
-                  {loadingRedis ? '扫描中...' : '无 Keys'}
+              {loadingRedis ? (
+                <div className="space-y-1 p-2">
+                  {Array.from({ length: 6 }, (_, i) => (
+                    <div key={i} className="flex items-center gap-2 px-2 py-1.5">
+                      <div className="w-3 h-3 bg-[var(--dg-bg-tertiary)] rounded animate-pulse" />
+                      <div className="h-3.5 bg-[var(--dg-bg-tertiary)] rounded animate-pulse flex-1" />
+                      <div className="h-3 bg-[var(--dg-bg-tertiary)] rounded animate-pulse w-10" />
+                    </div>
+                  ))}
                 </div>
+              ) : redisKeys.length === 0 ? (
+                <div className="p-3 text-xs text-[var(--dg-text-muted)] text-center">无 Keys</div>
               ) : (
                 <div className="divide-y divide-[var(--dg-border-light)]">
                   {redisKeys.map(k => (