Initial pass at unicorn pack.

internal/game/packs.go

@@ -1,9 +1,7 @@
 package game
 
 // Card packs are the selectable sets of pets and food a game is played with.
-// Turtle and Golden ship with full card data; Unicorn is declared here as
-// infrastructure (shown but not yet playable) so the lobby, views, and
-// deck-building all have a single source of truth to grow into.
+// Turtle, Golden, and Unicorn all ship with full six-tier card data.
 
 // PackInfo describes one selectable pack. Playable gates whether a lobby may
 // choose it and start a game with it.
@@ -21,7 +19,7 @@ const DefaultPack = "turtle"
 var Packs = []PackInfo{
 	{ID: "turtle", Name: "Turtle Pack", Emoji: "🐢", Playable: true},
 	{ID: "golden", Name: "Golden Pack", Emoji: "🥇", Playable: true},
-	{ID: "unicorn", Name: "Unicorn Pack", Emoji: "🦄", Playable: false},
+	{ID: "unicorn", Name: "Unicorn Pack", Emoji: "🦄", Playable: true},
 }
 
 // packByID looks up a pack, returning false if the id is unknown.