feat(P1/P2): 完成TDD开发及P1/P2设计文档

## 设计文档
- multi_role_permission_design: 多角色权限设计 (CONDITIONAL GO)
- audit_log_enhancement_design: 审计日志增强 (CONDITIONAL GO)
- routing_strategy_template_design: 路由策略模板 (CONDITIONAL GO)
- sso_saml_technical_research: SSO/SAML调研 (CONDITIONAL GO)
- compliance_capability_package_design: 合规能力包设计 (CONDITIONAL GO)

## TDD开发成果
- IAM模块: supply-api/internal/iam/ (111个测试)
- 审计日志模块: supply-api/internal/audit/ (40+测试)
- 路由策略模块: gateway/internal/router/ (33+测试)
- 合规能力包: gateway/internal/compliance/ + scripts/ci/compliance/

## 规范文档
- parallel_agent_output_quality_standards: 并行Agent产出质量规范
- project_experience_summary: 项目经验总结 (v2)
- 2026-04-02-p1-p2-tdd-execution-plan: TDD执行计划

## 评审报告
- 5个CONDITIONAL GO设计文档评审报告
- fix_verification_report: 修复验证报告
- full_verification_report: 全面质量验证报告
- tdd_module_quality_verification: TDD模块质量验证
- tdd_execution_summary: TDD执行总结

依据: Superpowers执行框架 + TDD规范

gateway/internal/router/engine/routing_engine.go

@@ -0,0 +1,63 @@
+package engine
+
+import (
+	"context"
+	"errors"
+
+	"lijiaoqiao/gateway/internal/router/strategy"
+)
+
+// ErrStrategyNotFound 策略未找到
+var ErrStrategyNotFound = errors.New("strategy not found")
+
+// RoutingMetrics 路由指标接口
+type RoutingMetrics interface {
+	// RecordSelection 记录路由选择
+	RecordSelection(provider string, strategyName string, decision *strategy.RoutingDecision)
+}
+
+// RoutingEngine 路由引擎
+type RoutingEngine struct {
+	strategies map[string]strategy.StrategyTemplate
+	metrics    RoutingMetrics
+}
+
+// NewRoutingEngine 创建路由引擎
+func NewRoutingEngine() *RoutingEngine {
+	return &RoutingEngine{
+		strategies: make(map[string]strategy.StrategyTemplate),
+		metrics:    nil,
+	}
+}
+
+// RegisterStrategy 注册路由策略
+func (e *RoutingEngine) RegisterStrategy(name string, template strategy.StrategyTemplate) {
+	e.strategies[name] = template
+}
+
+// SetMetrics 设置指标收集器
+func (e *RoutingEngine) SetMetrics(metrics RoutingMetrics) {
+	e.metrics = metrics
+}
+
+// SelectProvider 根据策略选择Provider
+func (e *RoutingEngine) SelectProvider(ctx context.Context, req *strategy.RoutingRequest, strategyName string) (*strategy.RoutingDecision, error) {
+	// 查找策略
+	tpl, ok := e.strategies[strategyName]
+	if !ok {
+		return nil, ErrStrategyNotFound
+	}
+
+	// 执行策略选择
+	decision, err := tpl.SelectProvider(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+
+	// 记录指标
+	if e.metrics != nil && decision != nil {
+		e.metrics.RecordSelection(decision.Provider, decision.Strategy, decision)
+	}
+
+	return decision, nil
+}