identity: unify api.sx facade over audit + membership (+9 tests)

The identity coordinator now owns an audit ledger and a membership registry
alongside its token table (started with the ledger) and session registry.
login/logout are audited; new ops history/enroll/member_status/member_project
surface the audit and membership axes through the one `identity` door.
Identity proves who and reports membership; acl still decides permission.
Existing api behaviour unchanged. New tests/facade.sx. 177/177.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/identity/scoreboard.md

@@ -1,6 +1,6 @@
 # identity-on-sx Scoreboard
 
-**Total: 168 / 168 tests passing**
+**Total: 177 / 177 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -18,6 +18,7 @@
 | ✅ | clients | 11 | 11 |
 | ✅ | grants | 9 | 9 |
 | ✅ | device | 10 | 10 |
+| ✅ | facade | 9 | 9 |
 
 
 Generated by `lib/identity/conformance.sh`.