flow: remote-failover — try peers in order, fall through to local + 6 tests

(remote-failover addrs fn local) tries fn on each peer in order, moves to the next
on any raised error, and runs the local node if every peer fails. Threads input,
composes in sequences.

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

lib/flow/scoreboard.json

@@ -1,13 +1,13 @@
 {
-  "total": 81,
-  "passed": 81,
+  "total": 87,
+  "passed": 87,
   "failed": 0,
   "suites": {
     "basic": { "passed": 18, "total": 18 },
     "control": { "passed": 31, "total": 31 },
     "suspend": { "passed": 17, "total": 17 },
     "recovery": { "passed": 8, "total": 8 },
-    "distributed": { "passed": 7, "total": 7 }
+    "distributed": { "passed": 13, "total": 13 }
   },
   "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "in-progress" }
 }