feat: add equipment, achievements, and visual polish

- Equipment system: 12 items across weapon/armour/trinket slots with
  common/rare/epic/legendary rarities; starter commons auto-equipped,
  higher tiers drop from boss victories
- Achievement system: 15 milestones with typed conditions; checked
  each tick and crystal rewards applied automatically
- Achievement toast: slide-in notification, auto-dismisses after 4s
- Floating click text: +X gold floats on each manual click
- Expanded quests (9 total) and upgrades (12 total)
- Upgrade panel now shows locked upgrades so players can see their
  progression path
- formatNumber utility (K/M/B/T) used consistently across all panels
- Backfill logic for existing saves to add new content gracefully
- types package now emits .d.ts declarations

apps/api/src/data/initialState.ts

@@ -1,6 +1,8 @@
 import type { GameState, Player, PrestigeData } from "@elysium/types";
+import { DEFAULT_ACHIEVEMENTS } from "./achievements.js";
 import { DEFAULT_ADVENTURERS } from "./adventurers.js";
 import { DEFAULT_BOSSES } from "./bosses.js";
+import { DEFAULT_EQUIPMENT } from "./equipment.js";
 import { DEFAULT_QUESTS } from "./quests.js";
 import { DEFAULT_UPGRADES } from "./upgrades.js";
 
@@ -28,6 +30,8 @@ export const INITIAL_GAME_STATE = (player: Player, characterName: string): GameS
   upgrades: structuredClone(DEFAULT_UPGRADES),
   quests: structuredClone(DEFAULT_QUESTS),
   bosses: structuredClone(DEFAULT_BOSSES),
+  equipment: structuredClone(DEFAULT_EQUIPMENT),
+  achievements: structuredClone(DEFAULT_ACHIEVEMENTS),
   prestige: INITIAL_PRESTIGE,
   baseClickPower: 1,
   lastTickAt: Date.now(),