feat(auth): insert user_owned provision record on self-hosted registration

[raghavyuva]

Summary

• Added createUserOwnedProvisionRecord(userId, organizationId, sshKeyId) to src/auth/user-setup.ts
• Called inside loadSSHCredentials after createMachineBillingEntry (only runs when config.selfHosted is true)
• Inserts a user_provision_details row with type='user_owned' and step='COMPLETED' so the Go API's IsServerUserOwned check returns true for BYOS machines

Why

IsServerUserOwned in the Go API queries user_provision_details to determine if a machine is user-owned. Without this row, all BYOS lifecycle operations (pause, resume, restart, status) fell through to the provisioned-machine Redis queue path and timed out with 504.

Behaviour

• Non-fatal: if the insert fails, the error is logged and registration continues unchanged
• Only fires for self-hosted instances (config.selfHosted = true)
• No schema changes (the user_provision_details table already exists with all required columns)

Test plan

• Register a new self-hosted user
• Confirm user_provision_details row exists with type='user_owned' and step='COMPLETED' for that user's machine
• Confirm BYOS lifecycle API routes (status, pause, resume, restart) work without 504

Related

Companion PR: nixopus/nixopus — feat/byos-lifecycle (Go API lifecycle routing + SSH/DB operations)