flow: remote-node via mock fed-sx transport + 7 tests (Phase 4 begins)

(remote-node addr fn) runs a node on a federation peer. Transport is the fed-sx
boundary, mocked by a peer registry (flow-peer-register!); raises
flow-remote-unreachable / flow-remote-no-fn. Composes with sequence/suspend/retry.
Also fixes conformance.sh to load remote.sx before api.sx.

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

lib/flow/scoreboard.json

@@ -1,12 +1,13 @@
 {
-  "total": 74,
-  "passed": 74,
+  "total": 81,
+  "passed": 81,
   "failed": 0,
   "suites": {
     "basic": { "passed": 18, "total": 18 },
     "control": { "passed": 31, "total": 31 },
     "suspend": { "passed": 17, "total": 17 },
-    "recovery": { "passed": 8, "total": 8 }
+    "recovery": { "passed": 8, "total": 8 },
+    "distributed": { "passed": 7, "total": 7 }
   },
-  "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "pending" }
+  "phases": { "phase1": "done", "phase2": "done", "phase3": "done", "phase4": "in-progress" }
 }