feat: add auto-adventurer prestige upgrade for post-prestige loop automation

Adds the Autonomous Recruitment prestige upgrade (50 runestones) which
unlocks an Auto-Adventurer toggle. When enabled, the tick engine
automatically purchases the highest-tier unlocked adventurer the player
can afford each frame, reducing the manual grind after prestige resets.

packages/types/src/interfaces/gameState.ts

@@ -79,6 +79,11 @@ interface GameState {
    */
   autoBoss?: boolean;
 
+  /**
+   * When true, the tick engine automatically purchases the highest-tier affordable adventurer.
+   */
+  autoAdventurer?: boolean;
+
   /**
    * Companion unlock and active selection state — optional for backwards compatibility.
    */