docs: update project context for test-oauth-client
Capture the post-merge identity-blocker-id contract in the labeler
context file. The merge of test-oauth-client introduced
`blocked_by(..., check_id)` skip rows for HTTP / subscription / crypto
"stage not run" lines, and 1f0a973 then made the blocker ID dynamic
(scanning the identity stage output for the first failing check) and
plumbed it into the report stage via
`CreateReportRunOptions::identity_blocker_id`. Document that as a Key
decision and mention the new helper in the pipeline.rs file blurb.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>