feat(run): startup + shutdown ping on both channels

Answers 'is it even running?' within seconds of 'atm run' — no waiting
30 min for heartbeat + no need for a live trigger to occur.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atm/main.py

@@ -282,6 +282,16 @@ def run_live(cfg, duration_s=None, capture_stub: bool = False) -> None:
     ]
     notifier = FanoutNotifier(backends, Path(cfg.dead_letter_path))
 
+    # Startup ping — confirms both channels work before the first bar closes.
+    from datetime import datetime
+    dur_note = f" duration={cfg.heartbeat_min:d}m heartbeat" if duration_s is None else f" duration={duration_s/3600:.2f}h"
+    notifier.send(Alert(
+        kind="heartbeat",
+        title="ATM started",
+        body=f"config={cfg.config_version}{dur_note} at {datetime.now().isoformat(timespec='seconds')}",
+    ))
+    audit.log({"event": "started", "config": cfg.config_version})
+
     start = time.monotonic()
     heartbeat_due = start + cfg.heartbeat_min * 60
     levels_extractor = None
@@ -337,6 +347,13 @@ def run_live(cfg, duration_s=None, capture_stub: bool = False) -> None:
                 heartbeat_due = time.time() + cfg.heartbeat_min * 60
             time.sleep(cfg.loop_interval_s)
     finally:
+        try:
+            notifier.send(Alert(
+                kind="heartbeat", title="ATM stopped",
+                body=f"after {time.monotonic() - start:.0f}s",
+            ))
+        except Exception:
+            pass
         notifier.stop()
         audit.close()