feat: 新增全局错误透传规则功能

支持管理员配置上游错误如何返回给客户端：
- 新增 ErrorPassthroughRule 数据模型和 Ent Schema
- 实现规则的 CRUD API（/admin/error-passthrough-rules）
- 支持按错误码、关键词匹配，支持 any/all 匹配模式
- 支持按平台过滤（anthropic/openai/gemini/antigravity）
- 支持透传或自定义响应状态码和错误消息
- 实现两级缓存（Redis + 本地内存）和多实例同步
- 集成到 gateway_handler 的错误处理流程
- 新增前端管理界面组件
- 新增单元测试覆盖核心匹配逻辑

优化：
- 移除 refreshLocalCache 中的冗余排序（数据库已排序）
- 后端 Validate() 增加匹配条件非空校验

backend/internal/repository/error_passthrough_repo.go

@@ -0,0 +1,178 @@
+package repository
+
+import (
+	"context"
+
+	"github.com/Wei-Shaw/sub2api/ent"
+	"github.com/Wei-Shaw/sub2api/ent/errorpassthroughrule"
+	"github.com/Wei-Shaw/sub2api/internal/model"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+type errorPassthroughRepository struct {
+	client *ent.Client
+}
+
+// NewErrorPassthroughRepository 创建错误透传规则仓库
+func NewErrorPassthroughRepository(client *ent.Client) service.ErrorPassthroughRepository {
+	return &errorPassthroughRepository{client: client}
+}
+
+// List 获取所有规则
+func (r *errorPassthroughRepository) List(ctx context.Context) ([]*model.ErrorPassthroughRule, error) {
+	rules, err := r.client.ErrorPassthroughRule.Query().
+		Order(ent.Asc(errorpassthroughrule.FieldPriority)).
+		All(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	result := make([]*model.ErrorPassthroughRule, len(rules))
+	for i, rule := range rules {
+		result[i] = r.toModel(rule)
+	}
+	return result, nil
+}
+
+// GetByID 根据 ID 获取规则
+func (r *errorPassthroughRepository) GetByID(ctx context.Context, id int64) (*model.ErrorPassthroughRule, error) {
+	rule, err := r.client.ErrorPassthroughRule.Get(ctx, id)
+	if err != nil {
+		if ent.IsNotFound(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return r.toModel(rule), nil
+}
+
+// Create 创建规则
+func (r *errorPassthroughRepository) Create(ctx context.Context, rule *model.ErrorPassthroughRule) (*model.ErrorPassthroughRule, error) {
+	builder := r.client.ErrorPassthroughRule.Create().
+		SetName(rule.Name).
+		SetEnabled(rule.Enabled).
+		SetPriority(rule.Priority).
+		SetMatchMode(rule.MatchMode).
+		SetPassthroughCode(rule.PassthroughCode).
+		SetPassthroughBody(rule.PassthroughBody)
+
+	if len(rule.ErrorCodes) > 0 {
+		builder.SetErrorCodes(rule.ErrorCodes)
+	}
+	if len(rule.Keywords) > 0 {
+		builder.SetKeywords(rule.Keywords)
+	}
+	if len(rule.Platforms) > 0 {
+		builder.SetPlatforms(rule.Platforms)
+	}
+	if rule.ResponseCode != nil {
+		builder.SetResponseCode(*rule.ResponseCode)
+	}
+	if rule.CustomMessage != nil {
+		builder.SetCustomMessage(*rule.CustomMessage)
+	}
+	if rule.Description != nil {
+		builder.SetDescription(*rule.Description)
+	}
+
+	created, err := builder.Save(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return r.toModel(created), nil
+}
+
+// Update 更新规则
+func (r *errorPassthroughRepository) Update(ctx context.Context, rule *model.ErrorPassthroughRule) (*model.ErrorPassthroughRule, error) {
+	builder := r.client.ErrorPassthroughRule.UpdateOneID(rule.ID).
+		SetName(rule.Name).
+		SetEnabled(rule.Enabled).
+		SetPriority(rule.Priority).
+		SetMatchMode(rule.MatchMode).
+		SetPassthroughCode(rule.PassthroughCode).
+		SetPassthroughBody(rule.PassthroughBody)
+
+	// 处理可选字段
+	if len(rule.ErrorCodes) > 0 {
+		builder.SetErrorCodes(rule.ErrorCodes)
+	} else {
+		builder.ClearErrorCodes()
+	}
+	if len(rule.Keywords) > 0 {
+		builder.SetKeywords(rule.Keywords)
+	} else {
+		builder.ClearKeywords()
+	}
+	if len(rule.Platforms) > 0 {
+		builder.SetPlatforms(rule.Platforms)
+	} else {
+		builder.ClearPlatforms()
+	}
+	if rule.ResponseCode != nil {
+		builder.SetResponseCode(*rule.ResponseCode)
+	} else {
+		builder.ClearResponseCode()
+	}
+	if rule.CustomMessage != nil {
+		builder.SetCustomMessage(*rule.CustomMessage)
+	} else {
+		builder.ClearCustomMessage()
+	}
+	if rule.Description != nil {
+		builder.SetDescription(*rule.Description)
+	} else {
+		builder.ClearDescription()
+	}
+
+	updated, err := builder.Save(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return r.toModel(updated), nil
+}
+
+// Delete 删除规则
+func (r *errorPassthroughRepository) Delete(ctx context.Context, id int64) error {
+	return r.client.ErrorPassthroughRule.DeleteOneID(id).Exec(ctx)
+}
+
+// toModel 将 Ent 实体转换为服务模型
+func (r *errorPassthroughRepository) toModel(e *ent.ErrorPassthroughRule) *model.ErrorPassthroughRule {
+	rule := &model.ErrorPassthroughRule{
+		ID:              int64(e.ID),
+		Name:            e.Name,
+		Enabled:         e.Enabled,
+		Priority:        e.Priority,
+		ErrorCodes:      e.ErrorCodes,
+		Keywords:        e.Keywords,
+		MatchMode:       e.MatchMode,
+		Platforms:       e.Platforms,
+		PassthroughCode: e.PassthroughCode,
+		PassthroughBody: e.PassthroughBody,
+		CreatedAt:       e.CreatedAt,
+		UpdatedAt:       e.UpdatedAt,
+	}
+
+	if e.ResponseCode != nil {
+		rule.ResponseCode = e.ResponseCode
+	}
+	if e.CustomMessage != nil {
+		rule.CustomMessage = e.CustomMessage
+	}
+	if e.Description != nil {
+		rule.Description = e.Description
+	}
+
+	// 确保切片不为 nil
+	if rule.ErrorCodes == nil {
+		rule.ErrorCodes = []int{}
+	}
+	if rule.Keywords == nil {
+		rule.Keywords = []string{}
+	}
+	if rule.Platforms == nil {
+		rule.Platforms = []string{}
+	}
+
+	return rule
+}