completeness: agent version tracking (register+heartbeat+card chip), rebuild stale /bin/NexusAgent (Aug3->current), backup pre-change

agents/agent.py

@@ -12,6 +12,7 @@ import socket
 import platform
 import subprocess
 import urllib.request
+AGENT_VERSION = "2.1.0"
 import urllib.parse
 import argparse
 
@@ -750,7 +751,8 @@ def main():
         "arch": arch,
         "ip": ip,
         "osName": f"{system_os} {platform.release()}",
-        "tags": node_tags
+        "tags": node_tags,
+        "agentVersion": AGENT_VERSION
     }
 
     if not quiet_mode:
@@ -785,7 +787,8 @@ def main():
                 "uptime": uptime,
                 "processCount": get_process_count(),
                 "tags": node_tags,
-                "heartbeatInterval": heartbeat_interval
+                "heartbeatInterval": heartbeat_interval,
+                "agentVersion": AGENT_VERSION
             }
 
             res = http_post(f"{server_url}/api/agent/heartbeat", heartbeat_payload)