Contests bug fix drive

+ [ ] Creation bugs (like +4min, tournament)
+ [ ] Wrong problem link - https://codeforces.com/contest/16781/problem/B -> https://codeforces.com/contest/1678/problem/B1
+ [ ] Show status indicator on left bar
+ [ ] Warning to exit, dont show back button
+ [ ] Countdown timer for setup/forfeiture
+ [ ] Activity feed - Submission/progression events (etc), Ready event, persist events, unified for all participants
+ [ ] Incomplete match history + DB Persistence, leaderboards
+ [ ] Spectator mode
+ [ ] Set time/score per question/overall
+ [ ] Submission integrity
+ [ ] Security-related issues (like `createRoomContest()` doesn't check `isHead()`)
+ [ ] Insufficient problem-handling not according to spec
+ [ ] Team assignment interface
+ [ ] Code Runner integration
+ [ ] Top-N group progression for bracket tournaments