fix(account): findTagsByEntryIds Map key 소문자로 통일 + null guard

JDBC driver마다 column alias의 대소문자를 다르게 반환할 수 있어
entryId → entry_id, tagName → tag_name 으로 소문자 통일.
NPE 방지를 위한 null 체크도 추가.

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

src/main/java/com/sb/web/account/service/AccountService.java

@@ -60,8 +60,10 @@ public class AccountService {
         List<Long> ids = entries.stream().map(AccountEntry::getId).toList();
         Map<Long, List<String>> tagsByEntry = new HashMap<>();
         for (Map<String, Object> row : mapper.findTagsByEntryIds(ids)) {
-            Long eid = ((Number) row.get("entryId")).longValue();
-            String name = (String) row.get("tagName");
+            Object rawId = row.get("entry_id");
+            String name = (String) row.get("tag_name");
+            if (rawId == null || name == null) continue;
+            Long eid = ((Number) rawId).longValue();
             tagsByEntry.computeIfAbsent(eid, k -> new ArrayList<>()).add(name);
         }
         return entries.stream()