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/AboutPanel.tsx

@@ -51,6 +51,10 @@ const HOW_TO_PLAY = [
     title: "📅 Daily Challenges",
     body: "Complete daily challenges for bonus rewards including gold, essence, crystals, and runestones. Challenges reset each day and vary in difficulty. Completing all daily challenges gives an extra bonus reward.",
   },
+  {
+    title: "📖 Codex",
+    body: "Defeating bosses, completing quests, acquiring equipment, hiring adventurers, purchasing upgrades, unlocking prestige upgrades, and discovering new zones all permanently unlock lore entries in the Codex. A badge appears on the Codex tab and a toast notification pops up each time new lore is discovered. Collect all 364 entries to build a complete picture of the world of Elysium.",
+  },
   {
     title: "☁️ Cloud Saves",
     body: "Your progress is automatically saved to the cloud every 30 seconds whilst you play. You can also force a manual save at any time using the sync button in the resource bar. Your save is protected by HMAC validation to ensure data integrity.",