feat: major content expansion with essence and crystal sinks

- 6 zones (up from 3): Shadow Marshes, Volcanic Depths, Astral Void
- 18 bosses (up from 4): 3 per zone with zone-based sequential unlock
- 24 quests (up from 9): 3-4 per zone, reorganised by zone
- 15 adventurer tiers (up from 10): Shadow Assassin through Divine Champion
- 28 equipment pieces (up from 12): boss drops + purchasable with essence/crystals
- 24 upgrades (up from 13): crystal-cost upgrades + new adventurer upgrades
- 22 achievements (up from 14): new milestones for bosses, quests, gold, armies
- Purchasable equipment system: buy items directly with essence or crystals
- Crystal-cost upgrades: spend crystals on global and click power boosts
- Zone-based boss progression: defeating a zone's last boss unlocks the next zone

packages/types/src/interfaces/Equipment.ts

@@ -22,4 +22,6 @@ export interface Equipment {
   owned: boolean;
   /** Whether this item is currently equipped (only one per type can be equipped) */
   equipped: boolean;
+  /** If set, this item can be purchased directly rather than obtained via boss drops */
+  cost?: { gold: number; essence: number; crystals: number };
 }

packages/types/src/interfaces/Upgrade.ts

@@ -16,6 +16,7 @@ export interface Upgrade {
   multiplier: number;
   costGold: number;
   costEssence: number;
+  costCrystals: number;
   purchased: boolean;
   unlocked: boolean;
 }