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>

.env.example

@@ -51,6 +51,8 @@ BLACKJACK_AUTOPLAY_THRESHOLD=15
 BLACKJACK_MIN_BET=1
 BLACKJACK_MAX_BET=500
 BLACKJACK_DEBT_LIMIT=1000      # max debt before betting disabled
+UNO_MIN_BET=10                 # minimum wager in euros
+UNO_POT_TAUNT_THRESHOLD=500   # pot size at which GogoBee starts taunting
 
 # ---- Space Groups (automatic room grouping for community-wide leaderboards) ----
 SPACE_GROUP_THRESHOLD=50       # % of smaller room's members that must overlap (1-100, default 50)