채널 카드 필터 UI, 캐시 초기화, 나라 필터 수정

- 채널 설명/태그 DB 컬럼 추가 및 백오피스 편집 기능
- 채널 드롭다운을 유튜브 아이콘 토글 카드로 변경 (데스크톱 최대 4개 표시, 스크롤)
- 모바일 홈탭 채널 카드 가로 스크롤
- region "나라" 값 필터 옵션에서 제외
- 관리자 캐시 초기화 버튼 및 API 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-java/src/main/java/com/tasteby/controller/AdminCacheController.java

@@ -0,0 +1,25 @@
+package com.tasteby.controller;
+
+import com.tasteby.security.AuthUtil;
+import com.tasteby.service.CacheService;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.Map;
+
+@RestController
+@RequestMapping("/api/admin")
+public class AdminCacheController {
+
+    private final CacheService cacheService;
+
+    public AdminCacheController(CacheService cacheService) {
+        this.cacheService = cacheService;
+    }
+
+    @PostMapping("/cache-flush")
+    public Map<String, Object> flushCache() {
+        AuthUtil.requireAdmin();
+        cacheService.flush();
+        return Map.of("ok", true);
+    }
+}

backend-java/src/main/java/com/tasteby/controller/ChannelController.java

@@ -76,6 +76,14 @@ public class ChannelController {
         return result;
     }
 
+    @PutMapping("/{id}")
+    public Map<String, Object> update(@PathVariable String id, @RequestBody Map<String, String> body) {
+        AuthUtil.requireAdmin();
+        channelService.update(id, body.get("description"), body.get("tags"));
+        cache.flush();
+        return Map.of("ok", true);
+    }
+
     @DeleteMapping("/{channelId}")
     public Map<String, Object> delete(@PathVariable String channelId) {
         AuthUtil.requireAdmin();

backend-java/src/main/java/com/tasteby/domain/Channel.java

@@ -14,6 +14,8 @@ public class Channel {
     private String channelId;
     private String channelName;
     private String titleFilter;
+    private String description;
+    private String tags;
     private int videoCount;
     private String lastVideoAt;
 }

backend-java/src/main/java/com/tasteby/mapper/ChannelMapper.java

@@ -21,4 +21,8 @@ public interface ChannelMapper {
     int deactivateById(@Param("id") String id);
 
     Channel findByChannelId(@Param("channelId") String channelId);
+
+    void updateDescriptionTags(@Param("id") String id,
+                                @Param("description") String description,
+                                @Param("tags") String tags);
 }

backend-java/src/main/java/com/tasteby/service/ChannelService.java

@@ -38,4 +38,8 @@ public class ChannelService {
     public Channel findByChannelId(String channelId) {
         return mapper.findByChannelId(channelId);
     }
+
+    public void update(String id, String description, String tags) {
+        mapper.updateDescriptionTags(id, description, tags);
+    }
 }