feat: multi-team orchestrator - topology UI, team management, flag randomizer, public submit + leaderboard

- panel/teams.py: create/start/stop teams with isolated ports+creds, per-team receivers with CHALLENGE_PORT/CONTAINER env, flag randomization, submit validation + leaderboard
- panel/main.py: /api/teams, /api/teams/{idx}/randomize, /api/flag/submit, /api/leaderboard, /api/public/teams, /submit page
- panel/static/submit.html: public flag submission UI for teams
- receiver: _ch_port/_ch_container read .env per team, container name overrides
- .gitignore: exclude teams/, .venv, __pycache__

receiver/challenges/Carbeat.py

@@ -11,7 +11,7 @@ class Carbeat(Challenge):
     flag_location    = 'flags/carbeat.txt'
     history_location = 'history/carbeat.txt'
 
-    _CONTAINER   = "carbeat_container"
+    _CONTAINER   = os.environ.get("CHALLENGE_CONTAINER_CARBEAT", "carbeat_container")
     _SERVICE_CMD = ["docker", "exec", "-i", _CONTAINER, "/home/ctfuser/chall/mybini"]
     _HEX_RE      = re.compile(r'^[0-9a-fA-F]+$')