feat: content expansion, prestige shop, and offline earnings improvements

- Expand content to 18 zones, 72 bosses, 95 quests, 32 adventurer tiers
- Add prestige shop with 24 runestone upgrades across 5 categories
- Add PrestigeUpgrade type, data files, API routes, and frontend panel
- Fix offline earnings to include equipment and runestone multipliers
- Add offline essence calculation alongside offline gold
- Update OfflineModal to display both gold and essence earned
- Add IDEAS.md for tracking planned features

apps/api/src/services/offlineProgress.ts

@@ -3,21 +3,32 @@ import type { GameState } from "@elysium/types";
 const MAX_OFFLINE_SECONDS = 8 * 60 * 60; // 8 hours
 
 /**
- * Calculates the gold earned whilst the player was offline.
+ * Calculates the gold and essence earned whilst the player was offline.
  * Capped at 8 hours to prevent exploit via system clock manipulation.
+ * Applies the same multipliers as the client-side tick engine.
  */
-export const calculateOfflineGold = (
+export const calculateOfflineEarnings = (
   state: GameState,
   nowMs: number,
-): { offlineGold: number; offlineSeconds: number } => {
+): { offlineGold: number; offlineEssence: number; offlineSeconds: number } => {
   const elapsedSeconds = Math.min(
     (nowMs - state.lastTickAt) / 1000,
     MAX_OFFLINE_SECONDS,
   );
 
-  const goldPerSecond = state.adventurers.reduce((total, adventurer) => {
+  const equipmentGoldMultiplier = (state.equipment ?? [])
+    .filter((e) => e.equipped)
+    .reduce((mult, e) => mult * (e.bonus.goldMultiplier ?? 1), 1);
+
+  const runestonesIncome = state.prestige.runestonesIncomeMultiplier ?? 1;
+  const runestonesEssence = state.prestige.runestonesEssenceMultiplier ?? 1;
+
+  let goldPerSecond = 0;
+  let essencePerSecond = 0;
+
+  for (const adventurer of state.adventurers) {
     if (!adventurer.unlocked || adventurer.count === 0) {
-      return total;
+      continue;
     }
 
     const upgradeMultiplier = state.upgrades
@@ -29,17 +40,27 @@ export const calculateOfflineGold = (
       )
       .reduce((mult, u) => mult * u.multiplier, 1);
 
-    return (
-      total +
+    const prestige = state.prestige.productionMultiplier;
+
+    goldPerSecond +=
       adventurer.goldPerSecond *
-        adventurer.count *
-        upgradeMultiplier *
-        state.prestige.productionMultiplier
-    );
-  }, 0);
+      adventurer.count *
+      upgradeMultiplier *
+      prestige *
+      runestonesIncome *
+      equipmentGoldMultiplier;
+
+    essencePerSecond +=
+      adventurer.essencePerSecond *
+      adventurer.count *
+      upgradeMultiplier *
+      prestige *
+      runestonesEssence;
+  }
 
   return {
     offlineGold: goldPerSecond * elapsedSeconds,
+    offlineEssence: essencePerSecond * elapsedSeconds,
     offlineSeconds: elapsedSeconds,
   };
 };