图片预览手机适配 + 正文图统一接入 lightbox

- lightbox：打开锁背景滚动（手机上背景不再跟着滑）、手机滑动左右翻页、
  dvh 跟随全面屏可视高度、关闭钮/角标走 safe-area、图片全宽无圆角
- 全局 capture 委托：时间线/详情页 v-html 正文里的图统一可点开预览，
  capture+stop 压住整卡跳转；thumbifyHtml 把原图地址留在 data-fullsrc，
  预览用原图而非 480w 缩略图；链接卡缩略图不劫持（点击仍是打开链接）

frontend/src/components/ImgLightbox.vue

@@ -3,27 +3,54 @@ import { onBeforeUnmount, watch } from 'vue'
 import { lightboxState as st, closeLightbox, stepLightbox } from '../lightbox'
 
 // 图片预览层：App.vue 全局挂一次。铺满全屏的暗底 + 居中大图，
-// 多图时左右箭头 / 方向键切换，角标显示第几张；Esc / 点空白收起。
+// 多图时左右箭头 / 方向键 / 手机滑动切换，角标显示第几张；Esc / 点空白收起。
 
 function onKey(e) {
   if (e.key === 'Escape') closeLightbox()
   if (e.key === 'ArrowLeft') stepLightbox(-1)
   if (e.key === 'ArrowRight') stepLightbox(1)
 }
+
+// 打开时锁住背景滚动（手机上尤其明显：否则手指滑动会带着页面一起动）
+let prevOverflow = ''
 watch(
   () => st.open,
   (v) => {
-    if (v) window.addEventListener('keydown', onKey)
-    else window.removeEventListener('keydown', onKey)
+    if (v) {
+      window.addEventListener('keydown', onKey)
+      prevOverflow = document.body.style.overflow
+      document.body.style.overflow = 'hidden'
+    } else {
+      window.removeEventListener('keydown', onKey)
+      document.body.style.overflow = prevOverflow
+    }
   }
 )
-onBeforeUnmount(() => window.removeEventListener('keydown', onKey))
+onBeforeUnmount(() => {
+  window.removeEventListener('keydown', onKey)
+  document.body.style.overflow = prevOverflow
+})
+
+// 手机滑动翻页：横向位移超 44px 且大于纵向位移才算一次滑动
+let touchX = 0
+let touchY = 0
+function onTouchStart(e) {
+  touchX = e.touches[0].clientX
+  touchY = e.touches[0].clientY
+}
+function onTouchEnd(e) {
+  const dx = e.changedTouches[0].clientX - touchX
+  const dy = e.changedTouches[0].clientY - touchY
+  if (Math.abs(dx) > 44 && Math.abs(dx) > Math.abs(dy) * 1.4 && st.list.length > 1) {
+    stepLightbox(dx < 0 ? 1 : -1)
+  }
+}
 </script>
 
 <template>
   <Teleport to="body">
     <Transition name="lb">
-      <div v-if="st.open" class="lb-overlay" @click="closeLightbox">
+      <div v-if="st.open" class="lb-overlay" @click="closeLightbox" @touchstart.passive="onTouchStart" @touchend.passive="onTouchEnd">
         <img
           class="lb-img"
           :src="st.list[st.index]"
@@ -124,28 +151,43 @@ onBeforeUnmount(() => window.removeEventListener('keydown', onKey))
 }
 
 @media (max-width: 640px) {
+  .lb-overlay {
+    /* 全面屏 URL 栏收展时 100vh 会偏大，dvh 跟随可视高度 */
+    align-items: center;
+  }
+
   .lb-img {
-    max-width: 96vw;
-    max-height: 74vh;
+    max-width: 100vw;
+    max-height: 74dvh;
+    border-radius: 0;
   }
 
   .lb-nav {
-    width: 38px;
-    height: 38px;
+    width: 40px;
+    height: 40px;
     font-size: 22px;
+    /* 悬浮在图片两侧半透明，可见但不抢戏 */
+    background: rgba(255, 255, 255, 0.12);
   }
 
   .lb-nav.prev {
-    left: 10px;
+    left: calc(8px + env(safe-area-inset-left));
   }
 
   .lb-nav.next {
-    right: 10px;
+    right: calc(8px + env(safe-area-inset-right));
   }
 
   .lb-close {
-    top: 10px;
-    right: 10px;
+    top: calc(10px + env(safe-area-inset-top));
+    right: calc(10px + env(safe-area-inset-right));
+    width: 42px;
+    height: 42px;
+  }
+
+  .lb-count {
+    bottom: calc(14px + env(safe-area-inset-bottom));
+    font-size: 12px;
   }
 }