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>

internal/db/db.go

@@ -621,6 +621,38 @@ CREATE TABLE IF NOT EXISTS api_cache (
 	cached_at INTEGER DEFAULT (unixepoch())
 );
 
+-- Euro economy
+CREATE TABLE IF NOT EXISTS euro_balances (
+	user_id      TEXT PRIMARY KEY,
+	balance      REAL NOT NULL DEFAULT 0,
+	updated_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS euro_transactions (
+	id           INTEGER PRIMARY KEY AUTOINCREMENT,
+	user_id      TEXT NOT NULL,
+	amount       REAL NOT NULL,
+	reason       TEXT NOT NULL,
+	created_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+CREATE INDEX IF NOT EXISTS idx_euro_tx_user ON euro_transactions(user_id, created_at);
+
+-- Hangman scores
+CREATE TABLE IF NOT EXISTS hangman_scores (
+	user_id       TEXT PRIMARY KEY,
+	total_earned  REAL NOT NULL DEFAULT 0,
+	games_played  INTEGER NOT NULL DEFAULT 0,
+	games_won     INTEGER NOT NULL DEFAULT 0
+);
+
+-- Blackjack scores
+CREATE TABLE IF NOT EXISTS blackjack_scores (
+	user_id       TEXT PRIMARY KEY,
+	total_earned  REAL NOT NULL DEFAULT 0,
+	games_played  INTEGER NOT NULL DEFAULT 0,
+	games_won     INTEGER NOT NULL DEFAULT 0
+);
+
 -- Moderation: strikes
 CREATE TABLE IF NOT EXISTS mod_strikes (
 	id           INTEGER PRIMARY KEY AUTOINCREMENT,