Add UNO game, hangman threading, DM room reuse, and gameplay fixes

- Add full UNO game plugin (1v1 vs bot via DM, community pot, bot personality)
- Move hangman into threads with direct reply guessing (no !hangman prefix needed)
- Fix DM room duplication by checking m.direct account data with in-memory cache
- Auto-draw when player has no playable cards instead of requiring manual draw
- Remove forced UNO call phase — players are penalized naturally if they forget
- Fix mutex held during network I/O in hangman start
- Fix infinite loop when both sides have no playable cards and deck is empty
- Fix Wild Draw Four penalty being skipped when UNO prompt triggered
- Fix hangman displayPhrase word boundary clarity (triple-wide gaps for spaces)
- Add UNO env vars, db tables, and README updates

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

main.go

@@ -112,6 +112,7 @@ func main() {
 	registry.Register(plugin.NewFlipPlugin(client))
 	registry.Register(plugin.NewHangmanPlugin(client, euroPlugin))
 	registry.Register(plugin.NewBlackjackPlugin(client, euroPlugin))
+	registry.Register(plugin.NewUnoPlugin(client, euroPlugin))
 
 	// Community
 	registry.Register(plugin.NewMilkCartonPlugin(client, ratePlugin))