Support deleting an avalanche center

[rchlfryn]

Summary

Deleting a tenant (avalanche center) currently has no cleanup step — tenant-scoped data (pages, settings, media, navigation, built-in pages, home pages, etc.) is left orphaned when the tenant record is deleted.

What's needed

1. Confirmation step — since this is very invasive, add a confirmation prompt that requires typing the avalanche center name before allowing deletion.
2. Cleanup hook — a beforeDelete hook that removes all tenant-scoped data before the tenant record itself is deleted. A prior implementation (deprovisionBeforeDelete) was started but removed in commit f074b15.

References

• Commit that removed the hook: f074b15
• Tenant collection config: src/collections/Tenants/index.ts