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__

.gitignore

@@ -7,5 +7,10 @@ receiver/lib
 receiver/lib64
 receiver/pyenv.cfg
 receiver/include
-receiver/pwntools-docreceiver/.venv/
+receiver/pwntools-doc
+receiver/.venv/
 panel/.env
+panel/__pycache__/
+teams/
+*.pid
+__pycache__/