feat(user): add unbind Bangumi account functionality and update related services

Author: LiggMax

flow-client/src/main/java/com/ligg/flowclient/controller/AccountController.java

@@ -127,7 +127,8 @@ public Result<BangumiBindVo> getBangumiBind(
     }
 
     /**
-     * 绑定 Bangumi 账号（需已登录 AnimeFlow，Body 传 OAuth 授权码 code）。
+     * 绑定 Bangumi 账号
+     * 需已登录 AnimeFlow，Body 传 OAuth 授权码 code。
      */
     @PostMapping("/oauth/bangumi/bind")
     @IpEndpointRateLimit(keyPrefix = "animeflow:account:bind-bangumi:ip:", seconds = 60, maxRequests = 10)
@@ -139,6 +140,19 @@ public Result<BangumiBindVo> bindBangumi(
         return Result.success(ResponseCode.SUCCESS, bindVo);
     }
 
+    /**
+     * 解绑当前账号绑定的 Bangumi 账号
+     * 删除关联的 OAuth 记录。
+     */
+    @PostMapping("/oauth/bangumi/unbind")
+    @IpEndpointRateLimit(keyPrefix = "animeflow:account:unbind-bangumi:ip:", seconds = 60, maxRequests = 10)
+    public Result<BangumiBindVo> unbindBangumi(
+            @RequestAttribute(AuthorizationInterceptor.ACCESS_TOKEN_REQUEST_ATTRIBUTE) String accessToken) {
+        Long userId = jwtTokenService.validateAccessToken(accessToken);
+        BangumiBindVo bindVo = userOauthService.unbindBangumi(userId);
+        return Result.success(ResponseCode.SUCCESS, bindVo);
+    }
+
     /**
      * 绑定邮箱并设置登录密码。
      */

flow-client/src/main/java/com/ligg/flowclient/service/UserOauthService.java

@@ -20,4 +20,11 @@ public interface UserOauthService {
      * Bangumi 第三方授权登录：已绑定则直接登录，未绑定则创建本地账号（邮箱/密码为空）并登录。
      */
     FlowTokenVo loginBangumi(String code, Platform platform);
+
+    /**
+     * 解绑当前用户绑定的 Bangumi 账号，删除 user_oauth 中的关联记录。
+     *
+     * @return 解绑后的绑定状态（始终为 {@link BangumiBindVo#notBound()}）
+     */
+    BangumiBindVo unbindBangumi(Long userId);
 }

flow-client/src/main/java/com/ligg/flowclient/service/impl/UserOauthServiceImpl.java

@@ -76,6 +76,16 @@ public BangumiBindVo bindBangumi(Long userId, String code) {
         return toBindVo(context.me());
     }
 
+    @Override
+    @Transactional(rollbackFor = Exception.class)
+    public BangumiBindVo unbindBangumi(Long userId) {
+        UserOauthEntity entity = findByUserAndPlatform(userId);
+        if (entity != null) {
+            userOauthMapper.deleteById(entity.getId());
+        }
+        return BangumiBindVo.notBound();
+    }
+
     @Override
     @Transactional(rollbackFor = Exception.class)
     public FlowTokenVo loginBangumi(String code, Platform platform) {