[QA] #533 언급 적은 식당 제외 필터 — 검증 통과, 회귀 테스트 추가

- 설계서(docs/design/533-min-mentions-filter/README.md) 대비 구현 일치 확인
  (backend RestaurantMapper video_count/min_mentions, frontend 필터 UI)
- dev API 실측: min_mentions 0/1/2/3/5/100 전 구간 경계 위반 0건
  (=2→116개, =3→36개, DISTINCT+서브쿼리 중복 없음, 기존 필터 조합 회귀 없음)
- passesMinMentions()를 lib/filters.ts로 추출(동작 변경 없음)하고
  frontend/__tests__/filters.test.ts 6케이스 추가(경계값/null 처리 등)
- 백엔드 빌드, tsc, 프론트 전체 jest(6 suites, 32 tests) 통과

Refs #533

frontend/src/app/page.tsx

@@ -15,6 +15,7 @@ import MyReviewsList from "@/components/MyReviewsList";
 import BottomSheet from "@/components/BottomSheet";
 import FilterSheet, { FilterOption } from "@/components/FilterSheet";
 import { getCuisineIcon, getPhosphorCuisineIcon } from "@/lib/cuisine-icons";
+import { passesMinMentions } from "@/lib/filters";
 import Icon from "@/components/Icon";
 import FoodIcon from "@/components/FoodIcon";
 import * as PhosphorIcons from "@phosphor-icons/react";
@@ -249,7 +250,7 @@ export default function Home() {
       if (channelFilter && !(r.channels || []).includes(channelFilter)) return false;
       if (cuisineFilter && !matchCuisineFilter(r.cuisine_type, cuisineFilter)) return false;
       if (priceFilter && !matchPriceGroup(r.price_range, priceFilter)) return false;
-      if (minMentions > 0 && (r.video_count ?? 0) < minMentions) return false;
+      if (!passesMinMentions(r.video_count, minMentions)) return false;
       if (countryFilter) {
         const parsed = parseRegion(r.region);
         if (!parsed || parsed.country !== countryFilter) return false;