feat: 移除“租户管理员为用户充值 / 每租户一套余额”能力：余额统一为全局用户余额

backend/app/services/tenant_join.go

@@ -265,14 +265,12 @@ func (t *tenant) JoinByInvite(ctx context.Context, tenantID, userID int64, invit
 
 		// 加入租户：默认 member + verified；与 tenant.AddUser 保持一致。
 		tu := &models.TenantUser{
-			TenantID:      tenantID,
-			UserID:        userID,
-			Role:          types.NewArray([]consts.TenantUserRole{consts.TenantUserRoleMember}),
-			Status:        consts.UserStatusVerified,
-			Balance:       0,
-			BalanceFrozen: 0,
-			CreatedAt:     now,
-			UpdatedAt:     now,
+			TenantID:  tenantID,
+			UserID:    userID,
+			Role:      types.NewArray([]consts.TenantUserRole{consts.TenantUserRoleMember}),
+			Status:    consts.UserStatusVerified,
+			CreatedAt: now,
+			UpdatedAt: now,
 		}
 		if err := tx.Create(tu).Error; err != nil {
 			if isUniqueViolation(err) {
@@ -430,14 +428,12 @@ func (t *tenant) AdminApproveJoinRequest(ctx context.Context, tenantID, operator
 
 		// 先落成员关系，再更新申请状态，保证“通过后一定能成为成员”（至少幂等）。
 		tu := &models.TenantUser{
-			TenantID:      tenantID,
-			UserID:        req.UserID,
-			Role:          types.NewArray([]consts.TenantUserRole{consts.TenantUserRoleMember}),
-			Status:        consts.UserStatusVerified,
-			Balance:       0,
-			BalanceFrozen: 0,
-			CreatedAt:     now,
-			UpdatedAt:     now,
+			TenantID:  tenantID,
+			UserID:    req.UserID,
+			Role:      types.NewArray([]consts.TenantUserRole{consts.TenantUserRoleMember}),
+			Status:    consts.UserStatusVerified,
+			CreatedAt: now,
+			UpdatedAt: now,
 		}
 		if err := tx.Create(tu).Error; err != nil && !isUniqueViolation(err) {
 			return err