persist: projections — fold stream into read model, incremental resume + 9 tests

project.sx: projection state {:value :seq}; persist/project folds the whole
stream, persist/project-resume folds only the tail so read models update
incrementally. Pure step (value event)->value. 37/37.

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

lib/persist/scoreboard.md

@@ -7,4 +7,5 @@ _Generated by `lib/persist/conformance.sh`_
 | event | 6 | 0 | 6 |
 | log | 9 | 0 | 9 |
 | kv | 13 | 0 | 13 |
-| **Total** | **28** | **0** | **28** |
+| project | 9 | 0 | 9 |
+| **Total** | **37** | **0** | **37** |