Create a challenge, share the link, compete with friends on country flag identification.

Live: https://kamalnrf-flag-quiz.val.run

1. Create a challenge — pick your name and number of flags
2. Share the /c/{id} link with friends
3. Everyone gets the same flags (seeded shuffle), so it's a fair fight
4. Per-challenge leaderboard shows who's on top

POST /challenge              → { name, rounds } → { id }
GET  /c/{id}                 → challenge page (HTML)
GET  /c/{id}/leaderboard     → scores for that challenge
POST /c/{id}/score           → submit { name, score, total, speed_bonus, streak_best }
GET  /quiz?n=5               → standalone random quiz (no challenge)

• 1 point per correct answer
• Up to 2 speed bonus points (faster = more)
• +1 streak bonus at 3+ consecutive correct
• 12-second timer per question