servers.proxmox_integration_id was created (migration 0001) without an ON DELETE
rule, although schema.ts asks for "set null", so with foreign keys on, deleting
an integration that a server was linked to failed with a constraint error.
The delete route now clears the four proxmox_* columns on those servers first
and records how many it unlinked in the audit entry. schema.ts notes the gap.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>