identity: membership state machine + per-app grant projection (17 tests)

membership.sx — coop membership as a guarded state machine
(none→pending→active→lapsed⇄active, any→revoked terminal); invalid
transitions return explicit {error, CurrentStatus}, never silent no-ops.
project(Subject, App) renders the one canonical state into a per-app claim
({member,Tier,App} / {pending,App} / {lapsed,App} / {denied,App} /
{non_member,App}) — identity reports what the membership is; acl decides
whether the app should honour it. New tests/membership.sx. 92/92.

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: 75 / 75 tests passing**
+**Total: 92 / 92 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -10,6 +10,7 @@
 | ✅ | api | 10 | 10 |
 | ✅ | oauth | 17 | 17 |
 | ✅ | sso | 10 | 10 |
+| ✅ | membership | 17 | 17 |
 
 
 Generated by `lib/identity/conformance.sh`.