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/web/src/components/ui/ResourceBar.tsx

@@ -1,23 +1,11 @@
 import type { Resource } from "@elysium/types";
+import { formatNumber } from "../../utils/format.js";
 
 interface ResourceBarProps {
   resources: Resource;
   prestigeCount: number;
 }
 
-const formatNumber = (value: number): string => {
-  if (value >= 1_000_000_000) {
-    return `${(value / 1_000_000_000).toFixed(2)}B`;
-  }
-  if (value >= 1_000_000) {
-    return `${(value / 1_000_000).toFixed(2)}M`;
-  }
-  if (value >= 1_000) {
-    return `${(value / 1_000).toFixed(2)}K`;
-  }
-  return value.toFixed(1);
-};
-
 export const ResourceBar = ({ resources, prestigeCount }: ResourceBarProps): React.JSX.Element => (
   <header className="resource-bar">
     <div className="resource">