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/ent/migrate/schema.go

@@ -309,6 +309,42 @@ var (
 			},
 		},
 	}
+	// ErrorPassthroughRulesColumns holds the columns for the "error_passthrough_rules" table.
+	ErrorPassthroughRulesColumns = []*schema.Column{
+		{Name: "id", Type: field.TypeInt64, Increment: true},
+		{Name: "created_at", Type: field.TypeTime, SchemaType: map[string]string{"postgres": "timestamptz"}},
+		{Name: "updated_at", Type: field.TypeTime, SchemaType: map[string]string{"postgres": "timestamptz"}},
+		{Name: "name", Type: field.TypeString, Size: 100},
+		{Name: "enabled", Type: field.TypeBool, Default: true},
+		{Name: "priority", Type: field.TypeInt, Default: 0},
+		{Name: "error_codes", Type: field.TypeJSON, Nullable: true, SchemaType: map[string]string{"postgres": "jsonb"}},
+		{Name: "keywords", Type: field.TypeJSON, Nullable: true, SchemaType: map[string]string{"postgres": "jsonb"}},
+		{Name: "match_mode", Type: field.TypeString, Size: 10, Default: "any"},
+		{Name: "platforms", Type: field.TypeJSON, Nullable: true, SchemaType: map[string]string{"postgres": "jsonb"}},
+		{Name: "passthrough_code", Type: field.TypeBool, Default: true},
+		{Name: "response_code", Type: field.TypeInt, Nullable: true},
+		{Name: "passthrough_body", Type: field.TypeBool, Default: true},
+		{Name: "custom_message", Type: field.TypeString, Nullable: true, Size: 2147483647},
+		{Name: "description", Type: field.TypeString, Nullable: true, Size: 2147483647},
+	}
+	// ErrorPassthroughRulesTable holds the schema information for the "error_passthrough_rules" table.
+	ErrorPassthroughRulesTable = &schema.Table{
+		Name:       "error_passthrough_rules",
+		Columns:    ErrorPassthroughRulesColumns,
+		PrimaryKey: []*schema.Column{ErrorPassthroughRulesColumns[0]},
+		Indexes: []*schema.Index{
+			{
+				Name:    "errorpassthroughrule_enabled",
+				Unique:  false,
+				Columns: []*schema.Column{ErrorPassthroughRulesColumns[4]},
+			},
+			{
+				Name:    "errorpassthroughrule_priority",
+				Unique:  false,
+				Columns: []*schema.Column{ErrorPassthroughRulesColumns[5]},
+			},
+		},
+	}
 	// GroupsColumns holds the columns for the "groups" table.
 	GroupsColumns = []*schema.Column{
 		{Name: "id", Type: field.TypeInt64, Increment: true},
@@ -950,6 +986,7 @@ var (
 		AccountGroupsTable,
 		AnnouncementsTable,
 		AnnouncementReadsTable,
+		ErrorPassthroughRulesTable,
 		GroupsTable,
 		PromoCodesTable,
 		PromoCodeUsagesTable,
@@ -989,6 +1026,9 @@ func init() {
 	AnnouncementReadsTable.Annotation = &entsql.Annotation{
 		Table: "announcement_reads",
 	}
+	ErrorPassthroughRulesTable.Annotation = &entsql.Annotation{
+		Table: "error_passthrough_rules",
+	}
 	GroupsTable.Annotation = &entsql.Annotation{
 		Table: "groups",
 	}