feat(search): 排序菜单新增「最近更新 ↓ / ↑」按日期排序

按 lastUpdated（YYYY-MM-DD）字符串比较实现升降序，
无日期的异常包固定排在最后。

frontend/src/views/SearchView.vue

@@ -12,7 +12,7 @@ const route = useRoute()
 
 const keyword = ref('')
 const statusFilter = ref('all') // all | warn | ok | ignored | broken
-const sortMode = ref('default') // default | versions-desc | size-desc
+const sortMode = ref('default') // default | versions-desc | size-desc | date-desc | date-asc
 const isMobile = ref(false)
 let debounceTimer = null
 
@@ -98,6 +98,14 @@ const filtered = computed(() => {
     list = [...list].sort((a, b) => b.versions - a.versions)
   } else if (sortMode.value === 'size-desc') {
     list = [...list].sort((a, b) => b.size - a.size)
+  } else if (sortMode.value === 'date-desc' || sortMode.value === 'date-asc') {
+    // lastUpdated 为 YYYY-MM-DD，字符串可比较；无日期的包（broken 等）固定排最后
+    const dir = sortMode.value === 'date-desc' ? -1 : 1
+    list = [...list].sort((a, b) => {
+      if (!a.lastUpdated) return 1
+      if (!b.lastUpdated) return -1
+      return a.lastUpdated.localeCompare(b.lastUpdated) * dir
+    })
   }
   return list
 })
@@ -196,6 +204,8 @@ async function onCleanConfirmed(res) {
               <div class="dd-item" :class="{ on: sortMode === 'default' }" @click="pickSort('default')">默认<span v-if="sortMode === 'default'" class="dd-check">✓</span></div>
               <div class="dd-item" :class="{ on: sortMode === 'versions-desc' }" @click="pickSort('versions-desc')">版本数 ↓<span v-if="sortMode === 'versions-desc'" class="dd-check">✓</span></div>
               <div class="dd-item" :class="{ on: sortMode === 'size-desc' }" @click="pickSort('size-desc')">占用大小 ↓<span v-if="sortMode === 'size-desc'" class="dd-check">✓</span></div>
+              <div class="dd-item" :class="{ on: sortMode === 'date-desc' }" @click="pickSort('date-desc')">最近更新 ↓<span v-if="sortMode === 'date-desc'" class="dd-check">✓</span></div>
+              <div class="dd-item" :class="{ on: sortMode === 'date-asc' }" @click="pickSort('date-asc')">最近更新 ↑<span v-if="sortMode === 'date-asc'" class="dd-check">✓</span></div>
             </div>
           </Transition>
         </div>