Fix 500 when deleting an application with device codes

Deleting an application left its oidc_device_codes orphaned, tripping the
FK constraint and raising SQLite3::ConstraintException. Unlike the other
child tables, oidc_device_codes had neither a dependent: :destroy
association nor an on_delete: :cascade FK, so any app that had started a
device-authorization flow could not be deleted (regardless of groups/users,
since a pending device code has a null user_id).

Add the missing has_many :oidc_device_codes, dependent: :destroy and a
migration to cascade at the DB level, mirroring application_user_claims.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LARKs4cVsGrvKCkKZhPcy6

app/models/application.rb

@@ -36,6 +36,7 @@ class Application < ApplicationRecord
   has_many :allowed_groups, through: :application_groups, source: :group
   has_many :application_user_claims, dependent: :destroy
   has_many :oidc_authorization_codes, dependent: :destroy
+  has_many :oidc_device_codes, dependent: :destroy
   has_many :oidc_access_tokens, dependent: :destroy
   has_many :oidc_refresh_tokens, dependent: :destroy
   has_many :oidc_user_consents, dependent: :destroy