feat(codes): mark a code dead once the owner confirms it in game

Game8 still lists Y1INABQB6DEX, 2BJ64QRZ7RT8 and PLDXIB886Y1S as active
Genshin codes after the game refused them. CODE_CHECKS records the
owner's in-game check; build-codes stamps the matching code confirmedDead,
and the Codes tab shows it expired: "Confirmed expired in game, 2026-10-20."

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/shared/codes.ts

@@ -12,6 +12,15 @@ export const RedeemCodeSchema = z.object({
     .regex(/^\d{4}-\d{2}-\d{2}$/)
     .nullable()
     .optional(),
+  /**
+   * The day the repository owner tried the code in game and it no longer
+   * worked (`codeChecks.ts`). Only ever "dead": the source still supplies the
+   * code, its reward and its link.
+   */
+  confirmedDead: z
+    .string()
+    .regex(/^\d{4}-\d{2}-\d{2}$/)
+    .optional(),
   firstObservedAt: z.string().datetime(),
   sourceUrl: z.string().url(),
 });