feat(im): Task 5 - IM REST Controller + Router + Wire 集成

IMController (REST API):
- GET /api/v1/im/conversations: 会话列表
- GET /api/v1/im/messages: 历史消息（游标分页）
- PUT /api/v1/im/conversations/:id/pin: 置顶/取消
- DELETE /api/v1/im/conversations/🆔 删除会话
- DELETE /api/v1/im/conversations/:id/messages: 清空记录
- GET /api/v1/im/messages/search: 全局搜索
- GET /api/v1/im/unread: 全局未读数

Wire 集成:
- IMSet Provider Set + wire.Bind 接口注入
- App struct 新增 IM 字段
- wire_gen.go 手动更新
- OfflinePusher 通过 SetOfflinePusher 注入 WS Handler

Made-with: Cursor

backend/go-service/app/im/provider.go

@@ -0,0 +1,60 @@
+package im
+
+import (
+	"github.com/echochat/backend/app/im/controller"
+	"github.com/echochat/backend/app/im/dao"
+	"github.com/echochat/backend/app/im/handler"
+	"github.com/echochat/backend/app/im/service"
+	"github.com/echochat/backend/pkg/ws"
+	"github.com/google/wire"
+	"github.com/redis/go-redis/v9"
+	"gorm.io/gorm"
+)
+
+// ProvideConversationDAO 创建 ConversationDAO 实例
+func ProvideConversationDAO(db *gorm.DB) *dao.ConversationDAO {
+	return dao.NewConversationDAO(db)
+}
+
+// ProvideMessageDAO 创建 MessageDAO 实例
+func ProvideMessageDAO(db *gorm.DB) *dao.MessageDAO {
+	return dao.NewMessageDAO(db)
+}
+
+// ProvideIMService 创建 IMService 实例
+// friendChecker 和 userInfoGetter 由 contact 模块的 FriendshipDAO 隐式实现
+func ProvideIMService(
+	convDAO *dao.ConversationDAO,
+	msgDAO *dao.MessageDAO,
+	pubsub *ws.PubSub,
+	rdb *redis.Client,
+	friendChecker service.FriendChecker,
+	userInfoGetter service.UserInfoGetter,
+) *service.IMService {
+	return service.NewIMService(convDAO, msgDAO, pubsub, rdb, friendChecker, userInfoGetter)
+}
+
+// ProvideIMEventHandler 创建 IM WS 事件处理器并注册事件到 Hub
+func ProvideIMEventHandler(imService *service.IMService, hub *ws.Hub) *handler.EventHandler {
+	return handler.NewEventHandler(imService, hub)
+}
+
+// ProvideOfflinePusher 创建离线消息推送器
+func ProvideOfflinePusher(imService *service.IMService, convDAO *dao.ConversationDAO, pubsub *ws.PubSub) *handler.OfflinePusher {
+	return handler.NewOfflinePusher(imService, convDAO, pubsub)
+}
+
+// ProvideIMController 创建 IM REST 控制器
+func ProvideIMController(imService *service.IMService) *controller.IMController {
+	return controller.NewIMController(imService)
+}
+
+// IMSet IM 模块 Wire Provider Set
+var IMSet = wire.NewSet(
+	ProvideConversationDAO,
+	ProvideMessageDAO,
+	ProvideIMService,
+	ProvideIMEventHandler,
+	ProvideOfflinePusher,
+	ProvideIMController,
+)