[Developer] #533 언급 적은 식당 제외 필터 (min_mentions + video_count)

- backend: findAll 응답에 video_count(strong/unknown 링크수) + min_mentions 서버필터
  - Restaurant.videoCount, RestaurantMapper(xml/iface), Service, Controller(+cache key)
- frontend: Restaurant.video_count 타입 + 데스크톱 툴바 "언급"(2/3/5회+) 클라 필터
- 검증: min_mentions=2→116, =3→36 (위반 0). 빌드/tsc 통과
- 설계서 docs/design/533-min-mentions-filter/README.md

Refs #533
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend-java/src/main/resources/mybatis/mapper/RestaurantMapper.xml

@@ -25,6 +25,7 @@
         <result property="hidden" column="hidden" javaType="java.lang.Boolean"/>
         <result property="hiddenReason" column="hidden_reason"/>
         <result property="verifiedAt" column="verified_at"/>
+        <result property="videoCount" column="video_count"/>
     </resultMap>
 
     <!-- ===== Queries ===== -->
@@ -33,7 +34,9 @@
         SELECT DISTINCT r.id, r.name, r.address, r.region, r.latitude, r.longitude,
                r.cuisine_type, r.price_range, r.google_place_id, r.tabling_url, r.catchtable_url,
                r.business_status, r.rating, r.rating_count, r.updated_at,
-               r.hidden, r.hidden_reason, r.verified_at
+               r.hidden, r.hidden_reason, r.verified_at,
+               (SELECT COUNT(*) FROM video_restaurants vrc
+                 WHERE vrc.restaurant_id = r.id AND vrc.relevance IN ('strong','unknown')) AS video_count
         FROM restaurants r
         <if test="channel != null and channel != ''">
             JOIN video_restaurants vr_f ON vr_f.restaurant_id = r.id
@@ -55,6 +58,10 @@
             <if test="channel != null and channel != ''">
                 AND c_f.channel_name = #{channel}
             </if>
+            <if test="minMentions != null and minMentions > 0">
+                AND (SELECT COUNT(*) FROM video_restaurants vrc
+                       WHERE vrc.restaurant_id = r.id AND vrc.relevance IN ('strong','unknown')) &gt;= #{minMentions}
+            </if>
         </where>
         ORDER BY r.updated_at DESC
         OFFSET #{offset} ROWS FETCH NEXT #{limit} ROWS ONLY