propagation: single registry drives all node references

New bin/netvm-registry.py parses NODES.md (node -> cdp_port); every
consumer reads from it instead of hardcoding:
- onboard-driver.py: CDP_PORTS dict -> registry lookup (new nodes work)
- muse-signin.py: hardcoded 9410 -> --node/--cdp-port args
- muse-chat-api.py: hardcoded ACCOUNTS -> registry-built
- agent-health.sh: hardcoded muse/pip blocks -> loop over all active
  nodes (646 and opm now get health coverage too)
NODES.md: record opm node (9440).

bin/onboard-driver.py

@@ -16,13 +16,21 @@ VM->bl SSH stdin pipe.
 Part of the cred onboarding module (front-door repo, docs/CRED-MODULE.md).
 """
 import argparse
+import importlib.util
 import json
 import subprocess
 import sys
 import urllib.request
 
 SIGNIN = "/home/super/Projects/NetVM/bin/muse-signin.py"
-CDP_PORTS = {"muse": "9410", "pip": "9420"}
+
+
+def _load_registry():
+    path = "/home/super/Projects/NetVM/bin/netvm-registry.py"
+    spec = importlib.util.spec_from_file_location("netvm_registry", path)
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
 
 
 def cdp_ok(port):
@@ -51,9 +59,10 @@ def main():
         print("ERROR: unsupported service/id_type "
               "(muse+email only for now)", file=sys.stderr)
         return 1
-    port = CDP_PORTS.get(args.node)
+    port = _load_registry().port_for(args.node)
     if not port:
-        print("ERROR: unknown node", file=sys.stderr)
+        print("ERROR: unknown node '%s' (not in NODES.md registry)"
+              % args.node, file=sys.stderr)
         return 1
 
     if args.dry_run:
@@ -69,7 +78,7 @@ def main():
         print("ERROR: no identifier on stdin", file=sys.stderr)
         return 1
 
-    cmd = [sys.executable, SIGNIN, "--email", identifier]
+    cmd = [sys.executable, SIGNIN, "--node", args.node, "--email", identifier]
     if args.step == "submit":
         if not code:
             print("ERROR: no code on stdin", file=sys.stderr)