Add bot defeat tracking, audit fixes, and README UNO section

Add !twinbeeboard command (GogoBee's trophy wall) with unified
bot_defeats table tracking losses across Blackjack, UNO solo, and
UNO multiplayer. Fix No Mercy audit bugs: wild card color choice
routing, bot Color Roulette double-advance, missing DM notifications
for roulette victims and 7-0 swap targets, autoplay Color Roulette
effect. Remove dead code. Update README with full UNO documentation.

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

internal/plugin/blackjack.go

@@ -868,6 +868,9 @@ func (p *BlackjackPlugin) recordBJScore(userID id.UserID, net float64) {
 		   games_won = games_won + ?`,
 		string(userID), net, won, net, won,
 	)
+	if net < 0 {
+		recordBotDefeat(userID, "blackjack")
+	}
 }
 
 func (p *BlackjackPlugin) bjDisplayName(userID id.UserID) string {