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.json

@@ -2,9 +2,10 @@
   "suites": {
     "event": {"pass": 6, "fail": 0},
     "log": {"pass": 9, "fail": 0},
-    "kv": {"pass": 13, "fail": 0}
+    "kv": {"pass": 13, "fail": 0},
+    "project": {"pass": 9, "fail": 0}
   },
-  "total_pass": 28,
+  "total_pass": 37,
   "total_fail": 0,
-  "total": 28
+  "total": 37
 }