feat(api-gateway): 添加content服务代理路由

main.go添加textbooks/chapters/knowledge-points/questions四组路由

config.go新增ContentServiceURL字段

docs: known-issues记录P4 content端到端验证经验

services/api-gateway/internal/config/config.go

@@ -14,6 +14,7 @@ type Config struct {
 	IamServiceURL     string
 	TeacherBffURL     string
 	CoreEduServiceURL string
+	ContentServiceURL string
 	OTLPEndpoint      string
 	LogLevel          string
 	DevMode           bool
@@ -29,6 +30,7 @@ func Load() *Config {
 		IamServiceURL:     getEnv("IAM_SERVICE_URL", "http://localhost:3002"),
 		TeacherBffURL:     getEnv("TEACHER_BFF_URL", "http://localhost:3003"),
 		CoreEduServiceURL: getEnv("CORE_EDU_SERVICE_URL", "http://localhost:3004"),
+		ContentServiceURL: getEnv("CONTENT_SERVICE_URL", "http://localhost:3005"),
 		OTLPEndpoint:      getEnv("OTEL_EXPORTER_OTLP_ENDPOINT", "http://localhost:4318"),
 		LogLevel:          getEnv("LOG_LEVEL", "info"),
 		DevMode:           getEnvBool("DEV_MODE", false),