Add passkey model layer

Related to #569927

What does this MR do and why?

Adds the passkey model layer

• Adds the :authentication_mode, :passkey_eligible, and :last_used_at columns with appropriate validation in the WebauthnRegistration table
• Connects to the User model via associations
• Updates the WebauthnRegistration factory

Database Review

Query Plans (Backwards-compatibility)

Table

has_many	Query Plan
Initial (:webauthn_registrations)	link
Post-migration (:webauthn_registrations)	link
Post-migration (:passkeys)	link

Local Migrations

bin/rails db:migrate

main: == [advisory_lock_connection] object_id: 156460, pg_backend_pid: 63025
main: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: migrating =========
main: -- add_column(:webauthn_registrations, :authentication_mode, :integer, {:default=>1, :null=>false})
main:    -> 0.0483s
main: -- add_column(:webauthn_registrations, :passkey_eligible, :boolean, {:default=>false, :null=>false})
main:    -> 0.0023s
main: -- add_column(:webauthn_registrations, :last_used_at, :datetime_with_timezone)
main:    -> 0.0071s
main: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: migrated (0.0631s) 
main: == [advisory_lock_connection] object_id: 156460, pg_backend_pid: 63025
ci: == [advisory_lock_connection] object_id: 156460, pg_backend_pid: 63026
ci: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: migrating =========
ci: -- add_column(:webauthn_registrations, :authentication_mode, :integer, {:default=>1, :null=>false})
ci:    -> 0.0086s
ci: -- add_column(:webauthn_registrations, :passkey_eligible, :boolean, {:default=>false, :null=>false})
ci:    -> 0.0028s
ci: -- add_column(:webauthn_registrations, :last_used_at, :datetime_with_timezone)
ci:    -> 0.0012s
ci: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: migrated (0.0233s) 
ci: == [advisory_lock_connection] object_id: 156460, pg_backend_pid: 63026

VERSION=20250926104422 bin/rails db:migrate:down:main && VERSION=20250926104422 bin/rails db:migrate:down:ci

main: == [advisory_lock_connection] object_id: 156160, pg_backend_pid: 64613
main: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: reverting =========
main: -- remove_column(:webauthn_registrations, :authentication_mode)
main:    -> 0.0413s
main: -- remove_column(:webauthn_registrations, :passkey_eligible)
main:    -> 0.0020s
main: -- remove_column(:webauthn_registrations, :last_used_at)
main:    -> 0.0022s
main: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: reverted (0.0521s) 
main: == [advisory_lock_connection] object_id: 156160, pg_backend_pid: 64613
ci: == [advisory_lock_connection] object_id: 156160, pg_backend_pid: 65283
ci: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: reverting =========
ci: -- remove_column(:webauthn_registrations, :authentication_mode)
ci:    -> 0.0559s
ci: -- remove_column(:webauthn_registrations, :passkey_eligible)
ci:    -> 0.0021s
ci: -- remove_column(:webauthn_registrations, :last_used_at)
ci:    -> 0.0020s
ci: == 20250926104422 AddPasskeyColumnsToWebauthnRegistrations: reverted (0.0775s) 
ci: == [advisory_lock_connection] object_id: 156160, pg_backend_pid: 65283

How to set up and validate locally

• Clone this branch & run migrations

bin/rails db:migrate

• Open a rails console

gdk rails console

• Create a user with a WebAuthn registration and verify model changes.

user = User.first
auth1 = user.webauthn_registrations.create!(
 name: '1Password',
 credential_xid: SecureRandom.hex,
 public_key: SecureRandom.hex,
 counter: 0
)

user.webauthn_registrations.size
user.passkeys.size

auth1.update!(authentication_mode: 'passwordless')
user.webauthn_registrations.size
user.passkeys.size

auth1.last_used_at
auth1.update_last_used_at!
auth1.last_used_at

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.