fix: 第16轮搜索审计修复 — all_not/group_negated分离 + _parse_primary重复组 + 错误显示

- Bug 2 (MEDIUM): all_not 混淆外部NOT与内部NOT，新增 group_negated
  字段区分，_pubmed_conditions 改用 pp.group_negated[idx] 替代 all_not
- Bug 1 (MEDIUM): _parse_primary 括号组内重复group赋值，只处理
  group_id < 0 的未分配terms，_parse_or_expr 增加 depth>0 守卫
- Bug 3 (MEDIUM): SearchView.vue 搜索错误显示为"no results"，
  新增 searchError ref + NResult 错误面板
- Bug 4 (LOW): literature.py UUID类型转换优化

frontend/src/components.d.ts

@@ -15,6 +15,7 @@ declare module 'vue' {
     NModal: typeof import('naive-ui')['NModal']
     NoteEditModal: typeof import('./components/notes/NoteEditModal.vue')['default']
     NotificationBell: typeof import('./components/common/NotificationBell.vue')['default']
+    NResult: typeof import('naive-ui')['NResult']
     PageSkeleton: typeof import('./components/common/PageSkeleton.vue')['default']
     RouterLink: typeof import('vue-router')['RouterLink']
     RouterView: typeof import('vue-router')['RouterView']

frontend/src/views/app/SearchView.vue

@@ -28,6 +28,7 @@ const sort = ref('date')
 const results = ref<LiteratureItem[]>([])
 const loading = ref(false)
 const searched = ref(false)
+const searchError = ref('')
 const savedPmids = ref<Set<number>>(new Set())
 
 // ── 筛选参数 ──
@@ -361,8 +362,11 @@ const { page, total, goToPage } = usePagination({
         delete keysetCursors.value[p + 1]
       }
       yearCounts.value = data.year_counts || []
+      searchError.value = ''
     } catch (e: any) {
       if (e?.name === 'CanceledError' || e?.code === 'ERR_CANCELED') return
+      results.value = []
+      searchError.value = '搜索失败，请检查网络或稍后重试'
       toast.apiError(e, '搜索失败，请重试')
     }
     finally {
@@ -897,7 +901,8 @@ const specialTags = computed(() => filterOptions.value?.special_tags || {})
       </div>
 
 	    <PageSkeleton :loading="loading && !results.length">
-      <NEmpty v-if="searched&&!loading&&!results.length" description="未找到匹配文献，尝试修改搜索条件" />
+      <NResult v-if="searchError" status="error" :title="searchError" description="可稍后重试或联系管理员" />
+      <NEmpty v-else-if="searched&&!loading&&!results.length" description="未找到匹配文献，尝试修改搜索条件" />
 
       <LiteratureCard
         v-for="item in results"