fix: 第11轮深度审计修复 — P0 keyset翻页崩溃 + P1布尔符语义/语法误报等16项修复

P0 (1项):
- keyset cursor: lit.title or "__NULL__" 空字符串误判为NULL导致后续翻页全空

P1 (6项):
- boolean_operator: 仅扫描depth=0的token，括号内AND/OR不再影响顶层操作符判定
- is_pubmed_syntax: 去除AND/OR/NOT检测的IGNORECASE(PubMed仅识别大写布尔符)
- _relevance_query: MeSH-only查询(如breast[MAJR])补充原始回退，避免退化到日期排序
- pmid_terms: 缺少try/except int()，补充ValueError+DOI兜底
- 部分日期展开: 2024-01[DP]等YYYY-MM partial date展开为整月范围(DP/EDAT/CRDT)
- 前端#N去重: resolveQuery/expandQuery dedup refs防重复引用误判为循环

P2 (9项):
- cache: filter-options加入invalidate_search_cache清理
- worker: daily_ftp_update/daily_citation_update异常时finally保证缓存清理
- cursor_val: 空字符串''通过is None检查，补充not cursor_val
- keyset UI: 模板条件sort==='date'改为KEYSET_SORTS.has(sort)
- resetAllFilters: 补充showCustomYear=false

frontend/src/composables/useSearchHistory.ts

@@ -41,7 +41,8 @@ export function expandQuery(query: string, entries: HistoryEntry[]): string {
     if (current === prev) break
     const refs = current.match(/#(\d+)/g)
     if (refs) {
-      for (const ref of refs) {
+      const uniqueRefs = [...new Set(refs)]
+      for (const ref of uniqueRefs) {
         if (seen.has(ref)) return prev  // 循环引用 → 返回上次安全结果
         seen.add(ref)
       }