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>

internal/db/db.go

@@ -678,6 +678,25 @@ CREATE TABLE IF NOT EXISTS mod_actions (
 );
 CREATE INDEX IF NOT EXISTS idx_mod_actions_user ON mod_actions(user_id, taken_at);
 
+-- Uno
+CREATE TABLE IF NOT EXISTS uno_pot (
+	id          INTEGER PRIMARY KEY CHECK (id = 1),
+	balance     REAL NOT NULL DEFAULT 0,
+	updated_at  DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS uno_games (
+	id              INTEGER PRIMARY KEY AUTOINCREMENT,
+	player_id       TEXT NOT NULL,
+	wager           REAL NOT NULL,
+	result          TEXT NOT NULL,
+	pot_before      REAL NOT NULL,
+	pot_after       REAL NOT NULL,
+	turns           INTEGER NOT NULL,
+	started_at      DATETIME NOT NULL,
+	ended_at        DATETIME NOT NULL
+);
+
 -- Space groups (rooms with overlapping membership)
 CREATE TABLE IF NOT EXISTS space_groups (
 	room_id    TEXT PRIMARY KEY,