v0.3.1 - leaderboard auto-sync

• Opt in once (^Gtrophy publish --handle you); every unaided drill then syncs your ratings to the leaderboard automatically
• Offline drills never block on sync (5s timeout, quiet skip)
• ^Gtrophy publish --stop\ opts out of syncing
• Eligible-but-unregistered users get a one-line hint after drills
• Leaderboard: https://ashutosh-rath02.github.io/atrophy/leaderboard.html