fix(api,admin-ui,user-ui): add client token ttl controls and remove deprecated auth settings

[markwylde]

Summary

• preserve auth preview behavior by appending da_preview=1 in admin branding preview URLs and bypassing client existence checks in user login preview mode
• add per-client access token TTL support across API schema, admin client create/edit flows, and token issuance paths
• add migration 0014_client_access_token_ttl to persist client-level access token lifetimes
• remove deprecated auth setting surfaces (code, pkce, id_token, access_token) from settings update/list/seed/runtime config paths

Why

• preview URLs should render reliably without being blocked by runtime client checks
• token lifetimes now need to be controlled per client instead of deprecated global auth settings
• removing deprecated keys simplifies runtime config and admin settings behavior

Validation

• npm run tidy
• npm run build