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/plugin/flip.go

@@ -0,0 +1,80 @@
+package plugin
+
+import (
+	"math/rand/v2"
+
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/id"
+)
+
+// FlipPlugin handles !flip (coin flip) restricted to the games room.
+type FlipPlugin struct {
+	Base
+}
+
+func NewFlipPlugin(client *mautrix.Client) *FlipPlugin {
+	return &FlipPlugin{Base: Base{Client: client}}
+}
+
+func (p *FlipPlugin) Name() string { return "flip" }
+
+func (p *FlipPlugin) Commands() []CommandDef {
+	return []CommandDef{
+		{Name: "flip", Description: "Flip a coin", Usage: "!flip", Category: "Games"},
+		{Name: "games", Description: "List available games", Usage: "!games", Category: "Games"},
+	}
+}
+
+func (p *FlipPlugin) Init() error                        { return nil }
+func (p *FlipPlugin) OnReaction(_ ReactionContext) error { return nil }
+
+func (p *FlipPlugin) OnMessage(ctx MessageContext) error {
+	switch {
+	case p.IsCommand(ctx.Body, "flip"):
+		if !isGamesRoom(ctx.RoomID) {
+			gr := gamesRoom()
+			if gr != "" {
+				return p.SendReply(ctx.RoomID, ctx.EventID, "Games are only available in the games channel!")
+			}
+		}
+		return p.handleFlip(ctx)
+	case p.IsCommand(ctx.Body, "games"):
+		return p.handleGames(ctx)
+	}
+	return nil
+}
+
+func (p *FlipPlugin) handleFlip(ctx MessageContext) error {
+	if rand.IntN(2) == 0 {
+		return p.SendReply(ctx.RoomID, ctx.EventID, "🪙 **Heads!**")
+	}
+	return p.SendReply(ctx.RoomID, ctx.EventID, "🪙 **Tails!**")
+}
+
+func (p *FlipPlugin) handleGames(ctx MessageContext) error {
+	gr := gamesRoom()
+	roomNote := ""
+	if gr != "" {
+		roomNote = "\n\nAll games are played in the games channel."
+	}
+
+	return p.SendReply(ctx.RoomID, ctx.EventID,
+		"🎮 **Available Games**\n\n"+
+			"**!flip** — Coin flip\n"+
+			"**!hangman start** — Collaborative Hangman\n"+
+			"**!blackjack €amount** — Blackjack (1-2 players vs dealer)\n"+
+			"**!trivia** — Trivia questions\n\n"+
+			"**Economy:**\n"+
+			"**!balance** — Check your euros\n"+
+			"**!baltop** — Euro leaderboard\n"+
+			"**!baltransfer @user €amount** — Send euros\n"+
+			"**!hangboard** — Hangman leaderboard\n"+
+			"**!bjboard** — Blackjack leaderboard"+
+			roomNote)
+}
+
+// redirectToGamesRoom returns the room ID for games-restricted redirect.
+func redirectToGamesRoom(sender id.UserID) string {
+	_ = sender
+	return "Games are only available in the games channel!"
+}