Add blacksmith repair system, community lottery, and audit fixes

Blacksmith: equipment repair with tier-based pricing, DM confirmation flow,
masterwork/arena surcharges, full flavor text pools. Added to main adventure
menu as option 6 (rest bumped to 7).

Lottery: weekly draw (Friday 23:59 UTC), ticket purchases with 100/week cap,
Fisher-Yates number generation, fixed+jackpot prize tiers, community pot
funding, Thursday reminders, draw history.

Audit fixes: TOCTOU in blacksmith repair costs (recompute from fresh equipment),
user lock in DM slot selection, partial repair refund tracking, error logging
on save failures, Fisher-Yates bias correction, communityPotDebit return value
checks in draw execution.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.go

@@ -136,6 +136,8 @@ func main() {
 	registry.Register(adventurePlugin)
 	wordlePlugin := plugin.NewWordlePlugin(client, euroPlugin, dictClient)
 	registry.Register(wordlePlugin)
+	lotteryPlugin := plugin.NewLotteryPlugin(client, euroPlugin)
+	registry.Register(lotteryPlugin)
 
 	// Community
 	registry.Register(plugin.NewMilkCartonPlugin(client, ratePlugin))