feat: 在公告请求中添加参数校验，确保跳转链接长度不超过5000字符，并在创建和更新公告时应用有效性检查

src/main/java/com/gameplatform/server/controller/admin/AnnouncementController.java

@@ -11,6 +11,7 @@ import io.jsonwebtoken.Claims;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.Parameter;
 import io.swagger.v3.oas.annotations.tags.Tag;
+import javax.validation.Valid;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -35,7 +36,7 @@ public class AnnouncementController {
     
     @PostMapping
     @Operation(summary = "创建公告", description = "创建新的系统公告，belongId会自动从JWT token中获取")
-    public ResponseEntity<Object> createAnnouncement(@RequestBody AnnouncementRequest request, Authentication authentication) {
+    public ResponseEntity<Object> createAnnouncement(@Valid @RequestBody AnnouncementRequest request, Authentication authentication) {
         if (request.getTitle() == null || request.getTitle().trim().isEmpty()) {
             return ResponseEntity.badRequest().body(new Object() {
                 public final boolean success = false;
@@ -161,7 +162,7 @@ public class AnnouncementController {
     @Operation(summary = "更新公告", description = "更新指定ID的公告信息，belongId会自动从JWT token中获取")
     public ResponseEntity<Object> updateAnnouncement(
             @Parameter(description = "公告ID", example = "1") @PathVariable Long id,
-            @RequestBody AnnouncementRequest request,
+            @Valid @RequestBody AnnouncementRequest request,
             Authentication authentication) {
         
         // 检查公告是否存在

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

@@ -1,6 +1,7 @@
 package com.gameplatform.server.model.dto.admin;
 
 import io.swagger.v3.oas.annotations.media.Schema;
+import javax.validation.constraints.Size;
 
 @Schema(description = "公告请求DTO")
 public class AnnouncementRequest {
@@ -14,7 +15,8 @@ public class AnnouncementRequest {
     @Schema(description = "是否启用", required = true, example = "true")
     private Boolean enabled;
     
-    @Schema(description = "跳转链接", example = "https://example.com")
+    @Schema(description = "跳转链接（最大5000字符）", example = "https://example.com")
+    @Size(max = 5000, message = "跳转链接长度不能超过5000个字符")
     private String jumpUrl;
     
     // belongId字段保留用于内部设置，但不在API文档中暴露