perf(后端): 完成性能优化与连接池配置

新增 DB/Redis 连接池配置与校验，并补充单测

网关请求体大小限制与 413 处理

HTTP/req 客户端池化并调整上游连接池默认值

并发槽位改为 ZSET+Lua 与指数退避

用量统计改 SQL 聚合并新增索引迁移

计费缓存写入改工作池并补测试/基准

测试: 在 backend/ 下运行 go test ./...

backend/internal/repository/proxy_probe_service_test.go

@@ -34,22 +34,16 @@ func (s *ProxyProbeServiceSuite) setupProxyServer(handler http.HandlerFunc) {
 	s.proxySrv = httptest.NewServer(handler)
 }
 
-func (s *ProxyProbeServiceSuite) TestCreateProxyTransport_InvalidURL() {
-	_, err := createProxyTransport("://bad")
+func (s *ProxyProbeServiceSuite) TestProbeProxy_InvalidProxyURL() {
+	_, _, err := s.prober.ProbeProxy(s.ctx, "://bad")
 	require.Error(s.T(), err)
-	require.ErrorContains(s.T(), err, "invalid proxy URL")
+	require.ErrorContains(s.T(), err, "failed to create proxy client")
 }
 
-func (s *ProxyProbeServiceSuite) TestCreateProxyTransport_UnsupportedScheme() {
-	_, err := createProxyTransport("ftp://127.0.0.1:1")
+func (s *ProxyProbeServiceSuite) TestProbeProxy_UnsupportedProxyScheme() {
+	_, _, err := s.prober.ProbeProxy(s.ctx, "ftp://127.0.0.1:1")
 	require.Error(s.T(), err)
-	require.ErrorContains(s.T(), err, "unsupported proxy protocol")
-}
-
-func (s *ProxyProbeServiceSuite) TestCreateProxyTransport_Socks5SetsDialer() {
-	tr, err := createProxyTransport("socks5://127.0.0.1:1080")
-	require.NoError(s.T(), err, "createProxyTransport")
-	require.NotNil(s.T(), tr.DialContext, "expected DialContext to be set for socks5")
+	require.ErrorContains(s.T(), err, "failed to create proxy client")
 }
 
 func (s *ProxyProbeServiceSuite) TestProbeProxy_Success() {