Add games system: euro economy, Hangman, Blackjack, coin flip

Euro economy: virtual currency earned passively per message (tiered by
word count, 30s cooldown). Starting balance seeded from corpus character
count. Balance, leaderboard, and transfer commands. Debt system with
configurable limit.

Hangman: collaborative game with phrase pool loaded from file. ASCII
gallows display, tiered scoring (Easy/Medium/Hard/Extreme), early
solution bonus, participant tracking with DM verification. Community
phrase submission with LLM screening.

Blackjack: 1-2 players vs dealer. Standard casino rules (hit soft 17).
Auto-play on timeout. Bet validation against balance and debt limit.
Blackjack pays 1.5x. Separate leaderboard.

Games channel restriction: all game commands (trivia, hangman, blackjack,
flip) restricted to GAMES_ROOM. Dice (!roll) exempt. Trivia also
restricted.

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

main.go

@@ -106,6 +106,13 @@ func main() {
 	moviesPlugin := plugin.NewMoviesPlugin(client)
 	registry.Register(moviesPlugin)
 
+	// Games & Economy
+	euroPlugin := plugin.NewEuroPlugin(client)
+	registry.Register(euroPlugin)
+	registry.Register(plugin.NewFlipPlugin(client))
+	registry.Register(plugin.NewHangmanPlugin(client, euroPlugin))
+	registry.Register(plugin.NewBlackjackPlugin(client, euroPlugin))
+
 	// Community
 	registry.Register(plugin.NewMilkCartonPlugin(client, ratePlugin))
 	registry.Register(plugin.NewQuoteWallPlugin(client, ratePlugin))