feat: 增强用户端配置管理功能

主要修改:
1. 在SystemConfigController中完善用户端配置获取和批量更新接口的实现。
2. 优化SystemConfigService，增强配置值验证逻辑，确保配置的准确性和有效性。

技术细节:
- 新增的功能提升了用户端配置的管理灵活性，支持更高效的批量操作。

src/main/java/com/gameplatform/server/model/dto/admin/AnnouncementConverter.java

@@ -0,0 +1,43 @@
+package com.gameplatform.server.model.dto.admin;
+
+import com.gameplatform.server.model.entity.admin.Announcement;
+
+public class AnnouncementConverter {
+    
+    /**
+     * 将请求DTO转换为实体
+     */
+    public static Announcement toEntity(AnnouncementRequest request) {
+        if (request == null) {
+            return null;
+        }
+        
+        Announcement announcement = new Announcement();
+        announcement.setTitle(request.getTitle());
+        announcement.setContent(request.getContent());
+        announcement.setEnabled(request.getEnabled());
+        announcement.setJumpUrl(request.getJumpUrl());
+        
+        return announcement;
+    }
+    
+    /**
+     * 将实体转换为响应DTO
+     */
+    public static AnnouncementResponse toResponse(Announcement announcement) {
+        if (announcement == null) {
+            return null;
+        }
+        
+        AnnouncementResponse response = new AnnouncementResponse();
+        response.setId(announcement.getId());
+        response.setTitle(announcement.getTitle());
+        response.setContent(announcement.getContent());
+        response.setEnabled(announcement.getEnabled());
+        response.setJumpUrl(announcement.getJumpUrl());
+        response.setCreatedAt(announcement.getCreatedAt());
+        response.setUpdatedAt(announcement.getUpdatedAt());
+        
+        return response;
+    }
+}

src/main/java/com/gameplatform/server/model/dto/admin/AnnouncementRequest.java

@@ -0,0 +1,51 @@
+package com.gameplatform.server.model.dto.admin;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+@Schema(description = "公告请求DTO")
+public class AnnouncementRequest {
+    
+    @Schema(description = "公告标题", required = true, example = "系统维护通知")
+    private String title;
+    
+    @Schema(description = "公告内容", required = true, example = "系统将于今晚10点进行维护，预计维护时间2小时")
+    private String content;
+    
+    @Schema(description = "是否启用", required = true, example = "true")
+    private Boolean enabled;
+    
+    @Schema(description = "跳转链接", example = "https://example.com")
+    private String jumpUrl;
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getContent() {
+        return content;
+    }
+
+    public void setContent(String content) {
+        this.content = content;
+    }
+
+    public Boolean getEnabled() {
+        return enabled;
+    }
+
+    public void setEnabled(Boolean enabled) {
+        this.enabled = enabled;
+    }
+
+    public String getJumpUrl() {
+        return jumpUrl;
+    }
+
+    public void setJumpUrl(String jumpUrl) {
+        this.jumpUrl = jumpUrl;
+    }
+}

src/main/java/com/gameplatform/server/model/dto/admin/AnnouncementResponse.java

@@ -0,0 +1,85 @@
+package com.gameplatform.server.model.dto.admin;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+import java.time.LocalDateTime;
+
+@Schema(description = "公告响应DTO")
+public class AnnouncementResponse {
+    
+    @Schema(description = "公告ID", example = "1")
+    private Long id;
+    
+    @Schema(description = "公告标题", example = "系统维护通知")
+    private String title;
+    
+    @Schema(description = "公告内容", example = "系统将于今晚10点进行维护，预计维护时间2小时")
+    private String content;
+    
+    @Schema(description = "是否启用", example = "true")
+    private Boolean enabled;
+    
+    @Schema(description = "跳转链接", example = "https://example.com")
+    private String jumpUrl;
+    
+    @Schema(description = "创建时间")
+    private LocalDateTime createdAt;
+    
+    @Schema(description = "更新时间")
+    private LocalDateTime updatedAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getContent() {
+        return content;
+    }
+
+    public void setContent(String content) {
+        this.content = content;
+    }
+
+    public Boolean getEnabled() {
+        return enabled;
+    }
+
+    public void setEnabled(Boolean enabled) {
+        this.enabled = enabled;
+    }
+
+    public String getJumpUrl() {
+        return jumpUrl;
+    }
+
+    public void setJumpUrl(String jumpUrl) {
+        this.jumpUrl = jumpUrl;
+    }
+
+    public LocalDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(LocalDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public LocalDateTime getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(LocalDateTime updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+}