stage-9: heartbeat system with periodic checks

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

cli.py

@@ -405,6 +405,12 @@ def _cron_disable(name: str):
         print(f"Job '{name}' not found.")
 
 
+def cmd_heartbeat(args):
+    """Run heartbeat health checks."""
+    from src.heartbeat import run_heartbeat
+    print(run_heartbeat())
+
+
 def cmd_secrets(args):
     """Handle secrets subcommand."""
     if args.secrets_action == "set":
@@ -509,6 +515,9 @@ def main():
 
     secrets_sub.add_parser("test", help="Check required secrets")
 
+    # heartbeat
+    sub.add_parser("heartbeat", help="Run heartbeat health checks")
+
     # cron
     cron_parser = sub.add_parser("cron", help="Manage scheduled jobs")
     cron_sub = cron_parser.add_subparsers(dest="cron_action")
@@ -554,6 +563,7 @@ def main():
             cmd_channel(a) if a.channel_action else (channel_parser.print_help() or sys.exit(0))
         ),
         "send": cmd_send,
+        "heartbeat": cmd_heartbeat,
         "cron": lambda a: (
             cmd_cron(a) if a.cron_action else (cron_parser.print_help() or sys.exit(0))
         ),