feat(admin): 商品管理支持多选皮肤筛选且要求包含所选全部皮肤

- 后端过滤：将 AdminListQuery.SkinName 筛选逻辑对齐前台，由 OR(交集) 改为 AND(全包含)，选多款皮肤时账号必须同时包含所选的全部皮肤
- 前端交互：AdminListingsView 皮肤筛选支持多选交互，点击具体皮肤支持多选高亮，底部提供已选数量提示、清空与确定操作，外层按钮智能展示已选皮肤摘要
- 样式增强：补充管理后台皮肤筛选弹层底部的清空/确定操作栏样式
- 验证方式：新增并运行后端 TestFilterAdminListingsByMultipleSkinsRequiresAll 单元测试，运行全量 ./scripts/check.sh 门禁全绿通过

frontend/src/features/admin/views/AdminListingsView.vue

@@ -107,9 +107,29 @@ const assetFilterLabel = computed(() => {
     levelSlotLabel(filters.load || ''),
   ].join('/')
 })
-const skinFilterActive = computed(() => Boolean(filters.skin_group || filters.skin_name))
+const selectedSkinNames = computed<string[]>({
+  get() {
+    if (!filters.skin_name) return []
+    return filters.skin_name
+      .split(',')
+      .map(s => s.trim())
+      .filter(Boolean)
+  },
+  set(val: string[]) {
+    filters.skin_name = val.filter(Boolean).join(',')
+  },
+})
+
+const skinFilterActive = computed(() =>
+  Boolean(filters.skin_group || selectedSkinNames.value.length)
+)
 const skinFilterLabel = computed(() => {
-  if (filters.skin_name) return filters.skin_name
+  const names = selectedSkinNames.value
+  if (names.length === 1) return names[0]
+  if (names.length > 1) {
+    const joined = names.join('、')
+    return joined.length <= 14 ? joined : `${names[0]} 等${names.length}款`
+  }
   if (filters.skin_group) {
     return skinFilterGroups.value.find(group => group.key === filters.skin_group)?.title || '皮肤'
   }
@@ -299,17 +319,39 @@ function clearAssetFilters(shouldQuery = false) {
   if (shouldQuery) void queryListings()
 }
 
-function selectSkinFilter(group: string, name = '') {
-  filters.skin_group = group
-  filters.skin_name = name
+function isSkinNameActive(name: string) {
+  return selectedSkinNames.value.includes(name)
+}
+
+function toggleSkinNameFilter(name: string) {
+  const current = selectedSkinNames.value
+  if (current.includes(name)) {
+    selectedSkinNames.value = current.filter(item => item !== name)
+  } else {
+    selectedSkinNames.value = [...current, name]
+  }
+  filters.skin_group = ''
+}
+
+function selectSkinGroupFilter(groupKey: string) {
+  selectedSkinNames.value = []
+  filters.skin_group = filters.skin_group === groupKey ? '' : groupKey
   closeFilterPopover()
+  void queryListings()
+}
+
+function confirmSkinFilters() {
+  closeFilterPopover()
+  void queryListings()
 }
 
 function clearSkinFilters(shouldQuery = false) {
   filters.skin_group = ''
   filters.skin_name = ''
-  closeFilterPopover()
-  if (shouldQuery) void queryListings()
+  if (shouldQuery) {
+    closeFilterPopover()
+    void queryListings()
+  }
 }
 
 function insuranceSlotLabel(value: string) {
@@ -865,8 +907,8 @@ function formatQuantity(value: number) {
                 <button
                   class="admin-filter-reset"
                   type="button"
-                  :class="{ active: !filters.skin_group && !filters.skin_name }"
-                  @click="clearSkinFilters()"
+                  :class="{ active: !filters.skin_group && !selectedSkinNames.length }"
+                  @click="clearSkinFilters(true)"
                 >
                   全部皮肤
                 </button>
@@ -880,8 +922,10 @@ function formatQuantity(value: number) {
                     <strong>{{ group.title }}</strong>
                     <button
                       type="button"
-                      :class="{ active: filters.skin_group === group.key && !filters.skin_name }"
-                      @click="selectSkinFilter(group.key)"
+                      :class="{
+                        active: filters.skin_group === group.key && !selectedSkinNames.length,
+                      }"
+                      @click="selectSkinGroupFilter(group.key)"
                     >
                       全部{{ group.title.replace('干员', '') }}
                     </button>
@@ -892,15 +936,24 @@ function formatQuantity(value: number) {
                       :key="`${group.key}-${skin}`"
                       type="button"
                       :class="{
-                        active: filters.skin_group === group.key && filters.skin_name === skin,
+                        active: isSkinNameActive(skin),
                       }"
-                      @click="selectSkinFilter(group.key, skin)"
+                      @click="toggleSkinNameFilter(skin)"
                     >
                       {{ skin }}
                     </button>
                   </div>
                 </div>
               </div>
+              <div class="admin-skin-filter-footer">
+                <span class="selected-hint">已选 {{ selectedSkinNames.length }} 款皮肤</span>
+                <div class="footer-actions">
+                  <el-button size="small" link @click="clearSkinFilters(false)">清空</el-button>
+                  <el-button size="small" type="primary" @click="confirmSkinFilters"
+                    >确定</el-button
+                  >
+                </div>
+              </div>
             </el-popover>
           </el-form-item>
         </el-form>