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/strategy/cost_based.go

@@ -0,0 +1,132 @@
+package strategy
+
+import (
+	"context"
+	"errors"
+	"sort"
+
+	"lijiaoqiao/gateway/internal/adapter"
+	gwerror "lijiaoqiao/gateway/pkg/error"
+)
+
+// ErrNoAffordableProvider 没有可负担的Provider
+var ErrNoAffordableProvider = errors.New("no affordable provider available")
+
+// CostBasedTemplate 成本优先策略模板
+// 选择成本最低的provider
+type CostBasedTemplate struct {
+	name               string
+	maxCostPer1KTokens float64
+	providers          map[string]adapter.ProviderAdapter
+}
+
+// CostParams 成本参数
+type CostParams struct {
+	// 最大成本 ($/1K tokens)
+	MaxCostPer1KTokens float64
+}
+
+// NewCostBasedTemplate 创建成本优先策略模板
+func NewCostBasedTemplate(name string, params CostParams) *CostBasedTemplate {
+	return &CostBasedTemplate{
+		name:               name,
+		maxCostPer1KTokens: params.MaxCostPer1KTokens,
+		providers:          make(map[string]adapter.ProviderAdapter),
+	}
+}
+
+// RegisterProvider 注册Provider
+func (t *CostBasedTemplate) RegisterProvider(name string, provider adapter.ProviderAdapter) {
+	t.providers[name] = provider
+}
+
+// Name 获取策略名称
+func (t *CostBasedTemplate) Name() string {
+	return t.name
+}
+
+// Type 获取策略类型
+func (t *CostBasedTemplate) Type() string {
+	return "cost_based"
+}
+
+// SelectProvider 选择成本最低的Provider
+func (t *CostBasedTemplate) SelectProvider(ctx context.Context, req *RoutingRequest) (*RoutingDecision, error) {
+	if len(t.providers) == 0 {
+		return nil, gwerror.NewGatewayError(gwerror.ROUTER_NO_PROVIDER_AVAILABLE, "no provider registered")
+	}
+
+	// 收集所有可用provider的候选列表
+	type candidate struct {
+		name string
+		cost float64
+	}
+	var candidates []candidate
+
+	for name, provider := range t.providers {
+		// 检查provider是否支持该模型
+		supported := false
+		for _, m := range provider.SupportedModels() {
+			if m == req.Model || m == "*" {
+				supported = true
+				break
+			}
+		}
+		if !supported {
+			continue
+		}
+
+		// 检查健康状态
+		if !provider.HealthCheck(ctx) {
+			continue
+		}
+
+		// 获取成本信息 (实际实现需要从provider获取)
+		// 这里暂时设置为模拟值
+		cost := t.getProviderCost(provider)
+		candidates = append(candidates, candidate{name: name, cost: cost})
+	}
+
+	if len(candidates) == 0 {
+		return nil, gwerror.NewGatewayError(gwerror.ROUTER_NO_PROVIDER_AVAILABLE, "no available provider for model: "+req.Model)
+	}
+
+	// 按成本排序
+	sort.Slice(candidates, func(i, j int) bool {
+		return candidates[i].cost < candidates[j].cost
+	})
+
+	// 选择成本最低且在预算内的provider
+	maxCost := t.maxCostPer1KTokens
+	if req.MaxCost > 0 && req.MaxCost < maxCost {
+		maxCost = req.MaxCost
+	}
+
+	for _, c := range candidates {
+		if c.cost <= maxCost {
+			return &RoutingDecision{
+				Provider:        c.name,
+				Strategy:        t.Type(),
+				CostPer1KTokens: c.cost,
+				TakeoverMark:    true, // M-008: 标记为接管
+			}, nil
+		}
+	}
+
+	return nil, ErrNoAffordableProvider
+}
+
+// CostAwareProvider 成本感知Provider接口
+type CostAwareProvider interface {
+	GetCostPer1KTokens() float64
+}
+
+// getProviderCost 获取Provider的成本
+func (t *CostBasedTemplate) getProviderCost(provider adapter.ProviderAdapter) float64 {
+	// 尝试类型断言获取成本
+	if cp, ok := provider.(CostAwareProvider); ok {
+		return cp.GetCostPer1KTokens()
+	}
+	// 默认返回0.5，实际应从provider元数据获取
+	return 0.5
+}