fix: 修复文本输入框超出容器边界

- input/textarea 添加 box-sizing: border-box
- card 添加 overflow: hidden 防止内容溢出

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

miniprogram/app.wxss

@@ -112,6 +112,7 @@ page {
   background: var(--card);
   border: 1rpx solid var(--line);
   box-shadow: var(--shadow);
+  overflow: hidden;
   transition: transform 0.22s ease, border-color 0.22s ease, box-shadow 0.22s ease;
 }
 
@@ -164,6 +165,7 @@ page {
 .input,
 .textarea {
   width: 100%;
+  box-sizing: border-box;
   min-height: 88rpx;
   border-radius: 16rpx;
   border: 1rpx solid rgba(125, 163, 204, 0.36);