monitor : temp GPU, conso watts, espace disque, heartbeat dispatcher

- nvidia-smi : +temperature.gpu + power.draw
- UI : tags °C / W / espace disque libre
- Dispatcher heartbeat toutes les 4s → point vert/rouge en haut du monitor
- Fix Docker SSH : copie + chmod 600 au démarrage (Bad owner)

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

scripts/dispatcher.py

@@ -329,9 +329,18 @@ def pop_queued_stitch() -> sqlite3.Row | None:
         ).fetchone()
 
 
+def write_heartbeat():
+    hb = DB_PATH.parent / "dispatcher.heartbeat"
+    try:
+        hb.write_text(_now_iso())
+    except Exception:
+        pass
+
+
 def main():
     print(f"cosma-qc dispatcher · DB={DB_PATH} · workers={[w['host'] for w in WORKERS]}")
     while True:
+        write_heartbeat()
         job = pop_queued()
         if job:
             print(f"→ job #{job['id']} ({job['auv']}/{job['gopro_serial']}/{job['segment_label']})")