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/routes/prestige.ts

@@ -1,9 +1,11 @@
-import type { GameState, PrestigeRequest } from "@elysium/types";
+import type { BuyPrestigeUpgradeRequest, GameState, PrestigeRequest } from "@elysium/types";
 import { Hono } from "hono";
 import { prisma } from "../db/client.js";
 import { authMiddleware } from "../middleware/auth.js";
+import { DEFAULT_PRESTIGE_UPGRADES } from "../data/prestigeUpgrades.js";
 import {
   buildPostPrestigeState,
+  computeRunestoneMultipliers,
   isEligibleForPrestige,
 } from "../services/prestige.js";
 
@@ -61,3 +63,60 @@ prestigeRouter.post("/", async (context) => {
     newPrestigeCount: newPrestigeData.count,
   });
 });
+
+prestigeRouter.post("/buy-upgrade", async (context) => {
+  const discordId = context.get("discordId") as string;
+  const body = await context.req.json<BuyPrestigeUpgradeRequest>();
+
+  const { upgradeId } = body;
+  if (!upgradeId) {
+    return context.json({ error: "upgradeId is required" }, 400);
+  }
+
+  const upgrade = DEFAULT_PRESTIGE_UPGRADES.find((u) => u.id === upgradeId);
+  if (!upgrade) {
+    return context.json({ error: "Unknown prestige upgrade" }, 404);
+  }
+
+  const record = await prisma.gameState.findUnique({ where: { discordId } });
+  if (!record) {
+    return context.json({ error: "No save found" }, 404);
+  }
+
+  const state = record.state as unknown as GameState;
+  const { purchasedUpgradeIds, runestones } = state.prestige;
+
+  if (purchasedUpgradeIds.includes(upgradeId)) {
+    return context.json({ error: "Upgrade already purchased" }, 400);
+  }
+
+  if (runestones < upgrade.runestonesCost) {
+    return context.json({ error: "Not enough runestones" }, 400);
+  }
+
+  const newRunestones = runestones - upgrade.runestonesCost;
+  const newPurchasedUpgradeIds = [...purchasedUpgradeIds, upgradeId];
+
+  const newState: GameState = {
+    ...state,
+    prestige: {
+      ...state.prestige,
+      runestones: newRunestones,
+      purchasedUpgradeIds: newPurchasedUpgradeIds,
+      ...computeRunestoneMultipliers(newPurchasedUpgradeIds),
+    },
+  };
+
+  await prisma.gameState.update({
+    where: { discordId },
+    data: { state: newState as object, updatedAt: Date.now() },
+  });
+
+  const multipliers = computeRunestoneMultipliers(newPurchasedUpgradeIds);
+
+  return context.json({
+    runestonesRemaining: newRunestones,
+    purchasedUpgradeIds: newPurchasedUpgradeIds,
+    ...multipliers,
+  });
+});