Add explicit RFC 8628 device login and oauth.flow selection while keeping
browser PKCE and the SDK runtime refresh path. Reuse issuer/resource
validation, configured client authentication and profile-scoped storage.
Only persist an approved, validated grant; never echo endpoint error bodies.
Slim redo of #104752 by @wjorgensen, replacing duplicate HTTP/storage
wrappers with the existing SDK and two real-wire invariant tests.
Refs #104742
Co-authored-by: Wes Hermes <weshermes@Wess-Mac-mini.localdomain>
Teknium