chore: record pre-existing uncommitted repository state

Snapshot of the in-flight state that already existed, identically, in both
this worktree and the main checkout before this session began: the initial
HTTP Client platform implementation (previously untracked), the redis-lab
removal, and the JPA / object-storage / notification integration work.

Kept separate from this session's HTTP Client review response, which lands
in the following commit, so the two bodies of work stay reviewable apart.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

infra/httpclient/oauth2/README.md

@@ -0,0 +1,12 @@
+# OAuth2 fixture
+
+`OAuth2Fixture` exposes a token endpoint backed by the same deterministic fixture server as the rest
+of the suite.
+
+It counts token requests, which is what makes design §20.3's single-flight guarantee provable rather
+than assumed: a hundred genuinely concurrent callers must produce exactly one token request. It can
+also issue rotating token values, so a stale cached token is detectable, and queue a failure status
+to exercise the refresh-failure path.
+
+The token endpoint is configured as its own Named Client Profile, separate from the upstream it
+issues tokens for.