fix(wish-tree): 修复切换树时导航栏消失问题

- Canvas添加z-index: 1，确保不覆盖导航栏
- top-bar添加pointer-events: none，子元素恢复auto
- WXML添加trees.length保护，防止空数组访问
- switchTree添加空数组保护

mini/pages/wish-tree/wish-tree.js

@@ -939,6 +939,8 @@ Page({
     const direction = e.currentTarget.dataset.direction;
     const { trees, currentTreeIndex } = this.data;
     
+    if (!trees.length) return;
+    
     let newIndex = currentTreeIndex;
     if (direction === 'prev') {
       newIndex = (currentTreeIndex - 1 + trees.length) % trees.length;

mini/pages/wish-tree/wish-tree.wxml

@@ -13,7 +13,7 @@
       <view class="switch-btn" bindtap="switchTree" data-direction="prev">
         <text class="switch-icon">‹</text>
       </view>
-      <view class="tree-name">{{trees[currentTreeIndex].name || '许愿树'}}</view>
+      <view class="tree-name">{{trees.length > 0 ? trees[currentTreeIndex].name : '许愿树'}}</view>
       <view class="switch-btn" bindtap="switchTree" data-direction="next">
         <text class="switch-icon">›</text>
       </view>

mini/pages/wish-tree/wish-tree.wxss

@@ -13,6 +13,7 @@
   left: 0;
   width: 100%;
   height: 100%;
+  z-index: 1;
 }
 
 /* 顶部导航 */
@@ -26,6 +27,11 @@
   justify-content: space-between;
   align-items: center;
   z-index: 100;
+  pointer-events: none;
+}
+
+.top-bar > * {
+  pointer-events: auto;
 }
 
 .tree-switcher {

mini/utils/core/index.js

@@ -269,14 +269,60 @@ function getConstellation(month, day) {
   }
 }
 
-/** 获取节气 */
+/** 计算某年某节气的公历日期（21世纪 C 值法，误差±1天） */
+function getSolarTermDate(year, termIndex) {
+  // 21世纪 C 值表（小寒=0, 大寒=1, 立春=2 ... 冬至=23）
+  const C21 = [
+    6.11, 20.84, 4.6295, 19.4599, 6.3826, 21.4155,  // 小寒 大寒 立春 雨水 惊蛰 春分
+    5.59, 20.888, 6.318, 21.86, 6.5, 22.20,          // 清明 谷雨 立夏 小满 芒种 夏至
+    7.928, 23.65, 8.35, 23.95, 8.44, 23.822,          // 小暑 大暑 立秋 处暑 白露 秋分
+    9.098, 24.218, 8.218, 23.08, 7.9, 22.60           // 寒露 霜降 立冬 小雪 大雪 冬至
+  ];
+  // 20世纪 C 值表
+  const C20 = [
+    6.9, 21.37, 5.4055, 20.12, 7.1082, 22.83,
+    6.38, 21.646, 7.108, 22.36, 7.5, 23.13,
+    8.318, 24.64, 9.35, 24.77, 9.74, 24.643,
+    9.878, 24.918, 9.11, 23.65, 8.8, 23.54
+  ];
+  const Y = year % 100;
+  const C = year >= 2000 ? C21[termIndex] : C20[termIndex];
+  // 闰年修正：小寒、大寒、立春、雨水（1-2月）
+  let leapAdjust = 0;
+  if (termIndex <= 3 && isLeapYear(year)) leapAdjust = 1;
+  // 特殊修正
+  if (year === 2026 && termIndex === 3) leapAdjust = -1; // 2026雨水
+  if (year === 2084 && termIndex === 3) leapAdjust = 1;
+  if (year === 1911 && termIndex === 6) leapAdjust = 1;  // 清明
+  if (year === 1984 && termIndex === 7) leapAdjust = -1; // 谷雨
+  if (year === 1911 && termIndex === 8) leapAdjust = 1;  // 立夏
+  if (year === 1981 && termIndex === 10) leapAdjust = -1; // 芒种
+  if (year === 1902 && termIndex === 11) leapAdjust = 1;  // 夏至
+  if (year === 1928 && termIndex === 12) leapAdjust = 1;  // 小暑
+  if (year === 1925 && termIndex === 13) leapAdjust = -1; // 大暑
+  if (year === 2002 && termIndex === 14) leapAdjust = 1;  // 立秋
+  if (year === 1927 && termIndex === 16) leapAdjust = 1;  // 白露
+  if (year === 1942 && termIndex === 17) leapAdjust = 1;  // 秋分
+  if (year === 2089 && termIndex === 18) leapAdjust = 1;  // 寒露
+  if (year === 2089 && termIndex === 19) leapAdjust = 1;  // 霜降
+  if (year === 1978 && termIndex === 20) leapAdjust = 1;  // 立冬
+  if (year === 1954 && termIndex === 21) leapAdjust = -1; // 小雪
+  if (year === 1918 && termIndex === 22) leapAdjust = 1;  // 大雪
+  if (year === 2021 && termIndex === 22) leapAdjust = -1;
+  if (year === 1902 && termIndex === 23) leapAdjust = 1;  // 冬至
+
+  return Math.floor(Y * 0.2422 + C) - Math.floor((Y - 1) / 4) + leapAdjust;
+}
+
+/** 获取节气（准确算法） */
 function getSolarTerm(year, month, day) {
-  const termDates = SOLAR_TERM_DATES[month - 1];
-  if (day === termDates[0]) {
-    return SOLAR_TERMS[(month - 1) * 2];
-  } else if (day === termDates[1]) {
-    return SOLAR_TERMS[(month - 1) * 2 + 1];
-  }
+  // 每月两个节气：第1个在 index (month-1)*2，第2个在 (month-1)*2+1
+  const idx1 = (month - 1) * 2;
+  const idx2 = idx1 + 1;
+  const d1 = getSolarTermDate(year, idx1);
+  const d2 = getSolarTermDate(year, idx2);
+  if (day === d1) return SOLAR_TERMS[idx1];
+  if (day === d2) return SOLAR_TERMS[idx2];
   return null;
 }