fix: include version in heartbeat payload so Workers tab shows real versions

Heartbeat was sending {} — version only appeared in registration.
Agents that never re-register (most of them) stayed NULL in the DB.
Now every heartbeat carries {"version": AGENT_VERSION} so agent.php
can update the column on every check-in.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent/jarvis-agent.py

@@ -434,7 +434,7 @@ def main():
 
         try:
             # Heartbeat + get commands
-            hb = api_post(f"{jarvis_url}/api/agent/heartbeat", {}, headers, ssl_verify=ssl_verify)
+            hb = api_post(f"{jarvis_url}/api/agent/heartbeat", {"version": AGENT_VERSION}, headers, ssl_verify=ssl_verify)
             if "error" in hb:
                 print(f"[WARN] Heartbeat failed: {hb['error']}", flush=True)
             else: