feat(billing): cap active users on an owner subscription

Super admin can set a seat limit of 3, 10, 20, or a negotiated number so an owner cannot add users past that cap.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/platform/platform.controller.ts

@@ -12,6 +12,7 @@ import { CurrentUser } from '../auth/current-user.decorator';
 import {
   ApplyBillingPlanDto,
   SetStorageQuotaDto,
+  SetUserCapDto,
   CreatePlatformAdminDto,
   CreatePlatformOrganizationDto,
   ResetPlatformAdminPasswordDto,
@@ -133,6 +134,16 @@ export class PlatformController {
     return this.platform.setStorageQuota(id, dto.quotaGb);
   }
 
+  @Get('users/:id/seats')
+  seatUsage(@Param('id') id: string) {
+    return this.platform.seatUsage(id);
+  }
+
+  @Patch('users/:id/billing/users')
+  setUserCap(@Param('id') id: string, @Body() dto: SetUserCapDto) {
+    return this.platform.setUserCap(id, dto.maxUsers);
+  }
+
   @Patch('organizations/:id/modules')
   updateOrganizationModules(
     @Param('id') id: string,