test(oauth-client): add interactive stage integration tests with happy-path + gating
Adds two new integration tests to oauth_client_interactive.rs:
1. interactive_happy_path_rp_drives_fake_as: Tests the full pipeline with
interactive stage driven by an in-process RelyingParty. Verifies
run_pipeline works with DriveRpInProcess drive mode.
2. interactive_partial_static_failure_blocks: Tests dependency gating by
constructing a StaticGating where dpop_bound_required fails, then
verifying that ClientReachedPar emits Skipped with blocked_by reason.
Covers AC5.3 / AC5.5.
Also updates all oauth_client_*.rs test files to include interactive: None
in OauthClientOptions initializers to match the new required field.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>