flow: crash recovery — store export/import + resumable scan + 8 tests (Phase 3 complete)

Records are name-keyed (defflow registers names); flow-store-export nulls live
procs to plain data, flow-store-import! restores, flow-resumable-ids scans for
paused flows. Resume re-resolves the proc by name, so a flow survives a wiped
store (simulated restart). The whole durable model persists only plain data.

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

lib/flow/scoreboard.json

@@ -1,11 +1,12 @@
 {
-  "total": 66,
-  "passed": 66,
+  "total": 74,
+  "passed": 74,
   "failed": 0,
   "suites": {
     "basic": { "passed": 18, "total": 18 },
     "control": { "passed": 31, "total": 31 },
-    "suspend": { "passed": 17, "total": 17 }
+    "suspend": { "passed": 17, "total": 17 },
+    "recovery": { "passed": 8, "total": 8 }
   },
-  "phases": { "phase1": "done", "phase2": "done", "phase3": "in-progress" }
+  "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "pending" }
 }