fix: correct environment variable name in sync scheduler

The scheduled sync was using AUTOTASK_INTEGRATION_CODE but the actual
environment variable is AUTOTASK_API_INTEGRATION_CODE. This caused
scheduled syncs to fail with 'IntegrationCode is invalid' while
manual syncs worked fine.

Changed:
- AUTOTASK_INTEGRATION_CODE -> AUTOTASK_API_INTEGRATION_CODE

This aligns the scheduler with autotask-factory.ts which was already
using the correct variable name.

lib/services/sync-scheduler.ts

@@ -43,7 +43,7 @@ class SyncScheduler {
       apiUrl: process.env.AUTOTASK_API_URL || '',
       username: process.env.AUTOTASK_USERNAME || '',
       password: process.env.AUTOTASK_SECRET || '',
-      apiIntegrationCode: process.env.AUTOTASK_INTEGRATION_CODE || '',
+      apiIntegrationCode: process.env.AUTOTASK_API_INTEGRATION_CODE || '',
     });
     this.syncService = createSyncService(autotaskClient);
   }