refactor(backend): P0 阻断修复 + 按最新修改时间收敛重复模块与契约

## P0 阻断修复
- 编译：修复实体类与服务类同名导致 Lombok 注解轮次中止的问题
  （MatchmakerService/CounselingService -> *Record），196 个编译错误归零
- 权限矩阵：platform_admin 按设计文档收紧为拒绝 5 项高危权限（不改测试阈值）
- 启动：修复 8 组 MyBatis-Plus 同名 bean 冲突（ConflictingBeanDefinition）
  与 URL 路由歧义（Ambiguous mapping），应用可正常启动

## 模块收敛（裁决规则：以文件修改时间为准）
- messaging 包整体删除，能力迁移至 chat 包
  * 会话列表/详情/未读端点、ConversationDTO、CursorPage
  * 消息游标分页统一为 { items, nextCursor }
- relationship 的 Match/UserRelation entity 与 mapper 合并进 match 包
- MatchmakerUserController 合并进 MatchmakerController，删除冗余 Controller
- 补齐 INV-004：chat sendText 增加双向 Block 校验，拉黑后禁止发送

## 契约对齐
- 红娘服务提交请求兼容前端 { requirement } 字段
- 消息与会话分页契约前后端统一

## 测试
- 迁移 6 个风控用例至 ChatSafetyServiceTest
- 清理 messaging 测试包遗留：6 个真实常量断言归位 chat 包，
  移除 2 个 assertTrue(true) 占位假测试（Block 真实行为已由
  P0FixVerificationTest / RelationshipBlockPriorityPhase08Test 覆盖）
- schema-h2.sql 对齐 PostgreSQL 真实表结构（matches 补列、
  conversation_members 改复合主键）

结果：290 tests, 0 failures, 0 errors, 3 skipped, BUILD SUCCESS

backend/src/test/resources/schema-h2.sql

@@ -14,6 +14,7 @@ CREATE TABLE user_relations (
 );
 CREATE TABLE matches (
   id VARCHAR(36) PRIMARY KEY, user_a_id VARCHAR(36), user_b_id VARCHAR(36), status VARCHAR(32), source VARCHAR(32),
+  source_id VARCHAR(64), last_activity_at TIMESTAMP WITH TIME ZONE, unmatched_by VARCHAR(36), episode INT,
   matched_at TIMESTAMP WITH TIME ZONE, unmatched_at TIMESTAMP WITH TIME ZONE, successful_at TIMESTAMP WITH TIME ZONE,
   created_at TIMESTAMP WITH TIME ZONE, updated_at TIMESTAMP WITH TIME ZONE, deleted_at TIMESTAMP WITH TIME ZONE
 );
@@ -27,11 +28,12 @@ CREATE TABLE conversations (
   last_message_at TIMESTAMP WITH TIME ZONE, created_at TIMESTAMP WITH TIME ZONE,
   updated_at TIMESTAMP WITH TIME ZONE, deleted_at TIMESTAMP WITH TIME ZONE
 );
+-- 复合主键 (conversation_id, user_id)，与 V004/V008 真实表结构一致，无 id 列
 CREATE TABLE conversation_members (
-  id VARCHAR(36) PRIMARY KEY, conversation_id VARCHAR(36), user_id VARCHAR(36), last_read_message_id VARCHAR(36),
-  unread_count INT, can_send BOOLEAN, created_at TIMESTAMP WITH TIME ZONE,
-  updated_at TIMESTAMP WITH TIME ZONE, deleted_at TIMESTAMP WITH TIME ZONE,
-  UNIQUE (conversation_id, user_id)
+  conversation_id VARCHAR(36), user_id VARCHAR(36), last_read_message_id VARCHAR(36),
+  unread_count INT, can_send BOOLEAN, joined_at TIMESTAMP WITH TIME ZONE,
+  created_at TIMESTAMP WITH TIME ZONE, updated_at TIMESTAMP WITH TIME ZONE, deleted_at TIMESTAMP WITH TIME ZONE,
+  PRIMARY KEY (conversation_id, user_id)
 );
 CREATE TABLE messages (
   id VARCHAR(36) PRIMARY KEY, conversation_id VARCHAR(36), sender_id VARCHAR(36), client_message_id VARCHAR(128),