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/game/AchievementPanel.tsx

@@ -0,0 +1,75 @@
+import type { Achievement } from "@elysium/types";
+import { useGame } from "../../context/GameContext.js";
+import { formatNumber } from "../../utils/format.js";
+
+const conditionDescription = (achievement: Achievement): string => {
+  const { condition } = achievement;
+  switch (condition.type) {
+    case "totalGoldEarned":
+      return `Earn ${formatNumber(condition.amount)} total gold`;
+    case "totalClicks":
+      return `Click ${formatNumber(condition.amount)} times`;
+    case "bossesDefeated":
+      return `Defeat ${condition.amount} boss${condition.amount > 1 ? "es" : ""}`;
+    case "questsCompleted":
+      return `Complete ${condition.amount} quest${condition.amount > 1 ? "s" : ""}`;
+    case "adventurerTotal":
+      return `Recruit ${formatNumber(condition.amount)} total adventurers`;
+    case "prestigeCount":
+      return `Prestige ${condition.amount} time${condition.amount > 1 ? "s" : ""}`;
+    case "equipmentOwned":
+      return `Own ${condition.amount} equipment item${condition.amount > 1 ? "s" : ""}`;
+  }
+};
+
+interface AchievementCardProps {
+  achievement: Achievement;
+}
+
+const AchievementCard = ({ achievement }: AchievementCardProps): React.JSX.Element => {
+  const isUnlocked = achievement.unlockedAt !== null;
+
+  return (
+    <div className={`achievement-card ${isUnlocked ? "unlocked" : "locked"}`}>
+      <div className="achievement-icon">{achievement.icon}</div>
+      <div className="achievement-info">
+        <h3>{achievement.name}</h3>
+        <p>{achievement.description}</p>
+        <p className="achievement-condition">{conditionDescription(achievement)}</p>
+        {achievement.reward?.crystals != null && (
+          <p className="achievement-reward">💎 +{achievement.reward.crystals} Crystals</p>
+        )}
+      </div>
+      <div className="achievement-status">
+        {isUnlocked ? (
+          <span className="achievement-unlocked-badge">✓ Unlocked</span>
+        ) : (
+          <span className="achievement-locked-badge">🔒</span>
+        )}
+      </div>
+    </div>
+  );
+};
+
+export const AchievementPanel = (): React.JSX.Element => {
+  const { state } = useGame();
+
+  if (!state) return <section className="panel"><p>Loading...</p></section>;
+
+  const achievements = state.achievements ?? [];
+  const unlocked = achievements.filter((a) => a.unlockedAt !== null).length;
+
+  return (
+    <section className="panel achievement-panel">
+      <h2>Achievements</h2>
+      <p className="achievement-progress">
+        {unlocked} / {achievements.length} unlocked
+      </p>
+      <div className="achievement-list">
+        {achievements.map((achievement) => (
+          <AchievementCard key={achievement.id} achievement={achievement} />
+        ))}
+      </div>
+    </section>
+  );
+};