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/api/client.ts

@@ -1,7 +1,7 @@
 import type {
   AuthResponse,
-  BossDamageRequest,
-  BossDamageResponse,
+  BossChallengeRequest,
+  BossChallengeResponse,
   LoadResponse,
   PrestigeRequest,
   PrestigeResponse,
@@ -61,10 +61,10 @@ export const saveGame = async (body: SaveRequest): Promise<SaveResponse> =>
     body: JSON.stringify(body),
   });
 
-export const dealBossDamage = async (
-  body: BossDamageRequest,
-): Promise<BossDamageResponse> =>
-  request<BossDamageResponse>("/boss/damage", {
+export const challengeBoss = async (
+  body: BossChallengeRequest,
+): Promise<BossChallengeResponse> =>
+  request<BossChallengeResponse>("/boss/challenge", {
     method: "POST",
     body: JSON.stringify(body),
   });