feat(13-02): register PAX8 as a toggleable integration-health row

- Add checkConfigOnly('pax8', 'PAX8', 'finance', [PAX8_CLIENT_ID, PAX8_CLIENT_SECRET]) call site
- Flows through existing applyDisableOverlay automatically for /admin/integrations

lib/services/integration-health.ts

@@ -345,6 +345,8 @@ export async function checkIntegrationHealth(opts?: { skipCache?: boolean }): Pr
       ['QBO_CLIENT_ID', 'QBO_CLIENT_SECRET'])),
     Promise.resolve(checkConfigOnly('appgate', 'AppGate SDP', 'security',
       ['APPGATE_URL', 'APPGATE_USERNAME', 'APPGATE_PASSWORD', 'APPGATE_DEVICE_ID'])),
+    Promise.resolve(checkConfigOnly('pax8', 'PAX8', 'finance',
+      ['PAX8_CLIENT_ID', 'PAX8_CLIENT_SECRET'])),
     Promise.resolve(checkConfigOnly('anthropic', 'Anthropic', 'llm',
       ['ANTHROPIC_API_KEY'])),
   ]);