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/bosses.ts

@@ -14,6 +14,7 @@ export const DEFAULT_BOSSES: Boss[] = [
     essenceReward: 25,
     crystalReward: 0,
     upgradeRewards: ["click_2"],
+    equipmentRewards: ["iron_sword", "chainmail", "mages_focus"],
     prestigeRequirement: 0,
   },
   {
@@ -29,6 +30,7 @@ export const DEFAULT_BOSSES: Boss[] = [
     essenceReward: 200,
     crystalReward: 10,
     upgradeRewards: ["global_2"],
+    equipmentRewards: ["enchanted_blade", "plate_armour", "arcane_orb"],
     prestigeRequirement: 0,
   },
   {
@@ -44,6 +46,7 @@ export const DEFAULT_BOSSES: Boss[] = [
     essenceReward: 1_000,
     crystalReward: 50,
     upgradeRewards: ["click_3"],
+    equipmentRewards: ["vorpal_sword", "dragon_scale"],
     prestigeRequirement: 1,
   },
   {
@@ -59,6 +62,7 @@ export const DEFAULT_BOSSES: Boss[] = [
     essenceReward: 5_000,
     crystalReward: 200,
     upgradeRewards: [],
+    equipmentRewards: ["philosophers_stone"],
     prestigeRequirement: 3,
   },
 ];