refactor: centralize custom interaction IDs into constants

Replace all hardcoded custom ID strings with module-level constants.
Each module now has *_CUSTOM_IDS in its types file, using functions
for dynamic IDs and PREFIX for startsWith matching.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot/modules/economy/shop.view.ts

@@ -19,6 +19,7 @@ import { existsSync } from "fs";
 import { LootType, EffectType } from "@shared/lib/constants";
 import type { LootTableItem } from "@shared/lib/types";
 import { getRarityConfig, defaultName, stripQuery } from "@shared/lib/rarity";
+import { SHOP_CUSTOM_IDS } from "./economy.types";
 
 export function getShopListingMessage(
     item: {
@@ -100,7 +101,7 @@ export function getShopListingMessage(
 
     // Create buy button (used in either main or loot container)
     const buyButton = new ButtonBuilder()
-        .setCustomId(`shop_buy_${item.id}`)
+        .setCustomId(SHOP_CUSTOM_IDS.BUY(item.id))
         .setLabel(`Purchase for ${item.price} 🪙`)
         .setStyle(ButtonStyle.Success)
         .setEmoji("🛒");