fix(runner): 延长媒体上游请求超时

图像生成上游同步响应可能超过 120 秒，原共享 HTTP 客户端会把仍在处理的提交标记为结果不确定。将客户端超时调整为 10 分钟，并增加回归测试；任务执行仍由现有租约、任务超时和取消机制约束。\n\n验证：\n- env -u AI_GATEWAY_TEST_DATABASE_URL go test ./internal/runner -run 'TestProviderHTTPClientTimeoutAllowsLongRunningMediaRequests|TestPlatformProxyMode' -count=1\n- env -u AI_GATEWAY_TEST_DATABASE_URL go test ./... -count=1

apps/api/internal/runner/proxy.go

@@ -19,6 +19,8 @@ type httpClientCache struct {
 	custom map[string]*http.Client
 }
 
+const providerHTTPClientTimeout = 10 * time.Minute
+
 func newHTTPClientCache() *httpClientCache {
 	return &httpClientCache{
 		none:   newHTTPClient(nil),
@@ -67,7 +69,7 @@ func newHTTPClient(proxy func(*http.Request) (*url.URL, error)) *http.Client {
 	transport := http.DefaultTransport.(*http.Transport).Clone()
 	transport.Proxy = proxy
 	return &http.Client{
-		Timeout:   120 * time.Second,
+		Timeout:   providerHTTPClientTimeout,
 		Transport: transport,
 	}
 }