flow: combinator library — tap, recover, map-flow + 11 tests (Phase 5 complete)

tap: side-effecting pass-through (returns input). recover: fail-VALUE counterpart
of try-catch (run node; on (fail r) run handler on r). map-flow: run a node over
each item of a list, join results sequentially. 116/116 across 7 suites.

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

lib/flow/scoreboard.json

@@ -1,6 +1,6 @@
 {
-  "total": 105,
-  "passed": 105,
+  "total": 116,
+  "passed": 116,
   "failed": 0,
   "suites": {
     "basic": { "passed": 18, "total": 18 },
@@ -8,7 +8,8 @@
     "suspend": { "passed": 17, "total": 17 },
     "recovery": { "passed": 8, "total": 8 },
     "distributed": { "passed": 19, "total": 19 },
-    "api": { "passed": 12, "total": 12 }
+    "api": { "passed": 12, "total": 12 },
+    "combinators": { "passed": 11, "total": 11 }
   },
-  "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "done", "phase5": "in-progress" }
+  "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "done", "phase5": "done" }
 }