feat(webhooks): manage inbound receiver lifecycle

[phucnguyen1707]

Summary

• add project-scoped PATCH and DELETE endpoints for inbound webhook receivers
• pause or resume receivers without changing their provider or shared secret
• atomically delete receivers with their event history while preventing cross-project mutations

Tests

• bun test tests/project-inbound-webhook-management.test.mjs — 3 passed
• full Node test suite — 168 passed
• npx tsc --noEmit
• npm run build