fix: preserve codex lore entries across prestige resets

apps/api/src/services/prestige.ts

@@ -111,6 +111,8 @@ export const buildPostPrestigeState = (
     ...freshState,
     prestige: newPrestigeData,
     lastTickAt: Date.now(),
+    // Codex lore persists across prestiges — players keep their discovered entries
+    ...(currentState.codex ? { codex: currentState.codex } : {}),
   };
 
   return { newState, newPrestigeData, runestonesEarned, milestoneRunestones };