feat: add codex / lore book with 364 entries

Implements a full in-game Codex panel that tracks lore discovery across
seven categories: bosses (72), quests (95), zones (18), equipment (65),
adventurer tiers (32), upgrades (57), and prestige upgrades (25).

Lore entries unlock automatically as players progress — existing
completions are retroactively and silently added on first load. New
discoveries trigger a toast notification and badge counter on the
Codex tab.

apps/web/src/components/game/CodexToast.tsx

@@ -0,0 +1,45 @@
+import { useEffect } from "react";
+import { CODEX_ENTRIES } from "../../data/codex.js";
+import { useGame } from "../../context/GameContext.js";
+
+interface CodexToastItemProps {
+  entryId: string;
+  onDismiss: (id: string) => void;
+}
+
+const CodexToastItem = ({ entryId, onDismiss }: CodexToastItemProps): React.JSX.Element | null => {
+  const entry = CODEX_ENTRIES.find((e) => e.id === entryId);
+
+  useEffect(() => {
+    const timer = setTimeout(() => {
+      onDismiss(entryId);
+    }, 4000);
+    return () => { clearTimeout(timer); };
+  }, [entryId, onDismiss]);
+
+  if (!entry) return null;
+
+  return (
+    <div className="codex-toast" onClick={() => { onDismiss(entryId); }}>
+      <span className="toast-icon">📖</span>
+      <div className="toast-content">
+        <span className="toast-label">✨ Lore Unlocked!</span>
+        <span className="toast-name">{entry.title}</span>
+      </div>
+    </div>
+  );
+};
+
+export const CodexToast = (): React.JSX.Element | null => {
+  const { newCodexEntryIds, dismissCodexEntry } = useGame();
+
+  if (newCodexEntryIds.length === 0) return null;
+
+  return (
+    <div className="achievement-toast-container">
+      {newCodexEntryIds.map((id) => (
+        <CodexToastItem key={id} entryId={id} onDismiss={dismissCodexEntry} />
+      ))}
+    </div>
+  );
+};