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/Warmup.py

@@ -1,5 +1,6 @@
 from .Challenge import Challenge
 
+import os
 import io
 import requests
 import random
@@ -30,7 +31,7 @@ class Warmup(Challenge):
             with open(self.flag_location, 'r') as f:
                 host_flag = f.read().strip()
             container_flag = subprocess.run([
-                "docker", "exec", "warmup_container", "cat", "/flag.txt"
+                "docker", "exec", os.environ.get("CHALLENGE_CONTAINER_WARMUP", "warmup_container"), "cat", "/flag.txt"
             ], capture_output=True, text=True).stdout.strip()
             assert host_flag == container_flag, 'Flag mismatch between host and container'