feat(themes): 新增主题模糊搜索接口及鉴权放行

支持按名称模糊搜索主题，并标记用户已购状态；同步放开 /themes/search 无需登录访问

src/main/java/com/yolo/keyborad/controller/ThemesController.java

@@ -91,4 +91,12 @@ public class ThemesController {
         return ResultUtils.success(result);
     }
 
+    @GetMapping("/search")
+    @Operation(summary = "搜索主题", description = "根据主题名称模糊搜索主题")
+    public BaseResponse<List<KeyboardThemesRespVO>> searchThemes(@RequestParam String themeName) {
+        Long userId = StpUtil.getLoginIdAsLong();
+        List<KeyboardThemesRespVO> result = themesService.searchThemesByName(themeName, userId);
+        return ResultUtils.success(result);
+    }
+
 }