fix: 搜索时folderId条件始终生效，根目录folderId为null则搜全部，子目录搜本目录

src/main/java/com/filesystem/service/FileService.java

@@ -48,8 +48,16 @@ public class FileService {
         wrapper.eq(FileEntity::getUserId, userId)
                .eq(FileEntity::getIsDeleted, 0);
         
-        // 有搜索关键词时：忽略 folderId，查用户所有文件
-        if (keyword == null || keyword.isEmpty()) {
+        boolean hasKeyword = keyword != null && !keyword.isEmpty();
+        
+        if (hasKeyword) {
+            // 有搜索关键词：根目录搜索查所有，子目录搜索限当前目录
+            if (folderId != null) {
+                wrapper.eq(FileEntity::getFolderId, folderId);
+            }
+            wrapper.like(FileEntity::getName, keyword);
+        } else {
+            // 无搜索关键词：正常浏览当前目录
             if (folderId != null) {
                 wrapper.eq(FileEntity::getFolderId, folderId);
             } else {
@@ -57,10 +65,6 @@ public class FileService {
             }
         }
         
-        if (keyword != null && !keyword.isEmpty()) {
-            wrapper.like(FileEntity::getName, keyword);
-        }
-        
         wrapper.orderByDesc(FileEntity::getIsFolder)
                .orderByDesc(FileEntity::getCreateTime);