persist: crash/restart recovery integration + migration notes — Phase 4 complete

recovery.sx: 6-test end-to-end crash/restart of an order ledger (log +
subscription kv read model + snapshot + compaction + invoice blob ref) on the
durable backend; everything survives a restart over the same disk + content
store, seq continues, two restarts converge. Migration notes (mem → durable
under a live subsystem) added to the plan. Roadmap done, 111/111.

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

lib/persist/scoreboard.md

@@ -14,4 +14,5 @@ _Generated by `lib/persist/conformance.sh`_
 | compaction | 11 | 0 | 11 |
 | durable | 15 | 0 | 15 |
 | blob | 14 | 0 | 14 |
-| **Total** | **105** | **0** | **105** |
+| recovery | 6 | 0 | 6 |
+| **Total** | **111** | **0** | **111** |