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/conformance.sh

@@ -24,6 +24,7 @@ SUITES=(
   "basic       flow-basic-tests-run!     lib/flow/tests/basic.sx"
   "control     flow-ctl-tests-run!       lib/flow/tests/control.sx"
   "suspend     flow-sus-tests-run!       lib/flow/tests/suspend.sx"
+  "recovery    flow-rec-tests-run!       lib/flow/tests/recovery.sx"
 )
 
 TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT