feat(首页头图): 按预产期推算星座，孕囊右下角挂「xx宝宝」玻璃小牌 (v26100424)

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

js/app.js

@@ -3,7 +3,7 @@
 (function () {
   'use strict';
   /* 页面版本号（YYMMDD+序号）：显示在「关于兜爸心选」页底部；bump 时同步 head 注释与 ?v= */
-  var VER = '26100423';
+  var VER = '26100424';
   const $ = (s, c) => (c || document).querySelector(s);
   const $$ = (s, c) => Array.from((c || document).querySelectorAll(s));
 
@@ -1219,7 +1219,8 @@
      syncPregnancy 有好几个提前 return 的分支，所以用微任务等它整个跑完再发，拿到的是最终状态。 */
   function pubPreg() {
     const d = { week: (state.postpartum || state.pregEmpty) ? null : state.week, day: state.day,
-      postpartum: !!state.postpartum, empty: !!state.pregEmpty };
+      postpartum: !!state.postpartum, empty: !!state.pregEmpty,
+      due: (state.due && !state.pregEmpty) ? [state.due.getFullYear(), state.due.getMonth() + 1, state.due.getDate()] : null };   // 2026-10-04 头图星座牌按预产期算
     window.__mbPreg = d;
     window.dispatchEvent(new CustomEvent('mb-preg', { detail: d }));
   }