feat(quota): 用户 × 平台 USD 配额

为用户在 anthropic/openai/gemini/antigravity 四个平台上提供日/周/月
三个窗口的 USD 配额管控。配额语义：未设置=不限制，0=禁用，>0=美元上限。

两层模型：
- 配置层：系统默认配额，以及 email/linuxdo/oidc/wechat/github/google/
  dingtalk 七个鉴权来源的默认配额，存于 settings，以嵌套 JSON 整体读写
  （系统 1 个 key + 每个来源 1 个 key），整体替换语义。
- 运行时层：user_platform_quota 表按用户记录实际配额，与配置层解耦。

后端：新增 ent schema 与 140_user_platform_quotas.sql 迁移、repository
与 service 端口、计费链路集成、管理端与用户端读写接口。
前端：管理端设置页配额编辑、用户配额管理 Modal、用户 Dashboard 展示、
中英文案。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/ent/intercept/intercept.go

@@ -42,6 +42,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/ent/userallowedgroup"
 	"github.com/Wei-Shaw/sub2api/ent/userattributedefinition"
 	"github.com/Wei-Shaw/sub2api/ent/userattributevalue"
+	"github.com/Wei-Shaw/sub2api/ent/userplatformquota"
 	"github.com/Wei-Shaw/sub2api/ent/usersubscription"
 )
 
@@ -992,6 +993,33 @@ func (f TraverseUserAttributeValue) Traverse(ctx context.Context, q ent.Query) e
 	return fmt.Errorf("unexpected query type %T. expect *ent.UserAttributeValueQuery", q)
 }
 
+// The UserPlatformQuotaFunc type is an adapter to allow the use of ordinary function as a Querier.
+type UserPlatformQuotaFunc func(context.Context, *ent.UserPlatformQuotaQuery) (ent.Value, error)
+
+// Query calls f(ctx, q).
+func (f UserPlatformQuotaFunc) Query(ctx context.Context, q ent.Query) (ent.Value, error) {
+	if q, ok := q.(*ent.UserPlatformQuotaQuery); ok {
+		return f(ctx, q)
+	}
+	return nil, fmt.Errorf("unexpected query type %T. expect *ent.UserPlatformQuotaQuery", q)
+}
+
+// The TraverseUserPlatformQuota type is an adapter to allow the use of ordinary function as Traverser.
+type TraverseUserPlatformQuota func(context.Context, *ent.UserPlatformQuotaQuery) error
+
+// Intercept is a dummy implementation of Intercept that returns the next Querier in the pipeline.
+func (f TraverseUserPlatformQuota) Intercept(next ent.Querier) ent.Querier {
+	return next
+}
+
+// Traverse calls f(ctx, q).
+func (f TraverseUserPlatformQuota) Traverse(ctx context.Context, q ent.Query) error {
+	if q, ok := q.(*ent.UserPlatformQuotaQuery); ok {
+		return f(ctx, q)
+	}
+	return fmt.Errorf("unexpected query type %T. expect *ent.UserPlatformQuotaQuery", q)
+}
+
 // The UserSubscriptionFunc type is an adapter to allow the use of ordinary function as a Querier.
 type UserSubscriptionFunc func(context.Context, *ent.UserSubscriptionQuery) (ent.Value, error)
 
@@ -1088,6 +1116,8 @@ func NewQuery(q ent.Query) (Query, error) {
 		return &query[*ent.UserAttributeDefinitionQuery, predicate.UserAttributeDefinition, userattributedefinition.OrderOption]{typ: ent.TypeUserAttributeDefinition, tq: q}, nil
 	case *ent.UserAttributeValueQuery:
 		return &query[*ent.UserAttributeValueQuery, predicate.UserAttributeValue, userattributevalue.OrderOption]{typ: ent.TypeUserAttributeValue, tq: q}, nil
+	case *ent.UserPlatformQuotaQuery:
+		return &query[*ent.UserPlatformQuotaQuery, predicate.UserPlatformQuota, userplatformquota.OrderOption]{typ: ent.TypeUserPlatformQuota, tq: q}, nil
 	case *ent.UserSubscriptionQuery:
 		return &query[*ent.UserSubscriptionQuery, predicate.UserSubscription, usersubscription.OrderOption]{typ: ent.TypeUserSubscription, tq: q}, nil
 	default: