identity: RFC 7662 full introspection metadata — introspect_full (+9 tests)

introspect_full returns {active, Subject, Client, Scope, Exp, Iat, bearer}
for live tokens and {inactive} otherwise — deepening the opaque-token /
live-lookup model. Access tokens now carry Iat (clock-at-issue); exp = iat +
ttl. Simple introspect is unchanged (all prior suites green). New
tests/introspect.sx. 210/210.

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: 201 / 201 tests passing**
+**Total: 210 / 210 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -22,6 +22,7 @@
 | ✅ | delegation | 8 | 8 |
 | ✅ | session-mgmt | 8 | 8 |
 | ✅ | exchange | 8 | 8 |
+| ✅ | introspect | 9 | 9 |
 
 
 Generated by `lib/identity/conformance.sh`.