feat(auth): implement decoupled sliding-window rate limiting for login and oauth

backend/plugins/domain/user/repository.go

@@ -18,8 +18,10 @@ import (
 )
 
 var (
-	dbMu  sync.RWMutex
-	dbSvc contracts.DBService
+	dbMu       sync.RWMutex
+	dbSvc      contracts.DBService
+	limiterMu  sync.RWMutex
+	limiterSvc contracts.LimiterService
 )
 
 // SetDBService sets the active DBService contract for the user domain plugin.
@@ -29,6 +31,13 @@ func SetDBService(s contracts.DBService) {
 	dbSvc = s
 }
 
+// SetLimiterService sets the active LimiterService contract for the user domain plugin.
+func SetLimiterService(s contracts.LimiterService) {
+	limiterMu.Lock()
+	defer limiterMu.Unlock()
+	limiterSvc = s
+}
+
 func getDB(ctx context.Context) *gorm.DB {
 	if s, err := core.InjectFrom[contracts.DBService](ctx); err == nil && s != nil {
 		return s.DB(ctx)
@@ -44,6 +53,17 @@ func getDB(ctx context.Context) *gorm.DB {
 	return nil
 }
 
+func getLimiter(ctx context.Context) contracts.LimiterService {
+	if s, err := core.InjectFrom[contracts.LimiterService](ctx); err == nil && s != nil {
+		return s
+	}
+
+	limiterMu.RLock()
+	s := limiterSvc
+	limiterMu.RUnlock()
+	return s
+}
+
 // GetUserByID 通过 ID 获取用户
 func GetUserByID(ctx context.Context, id uint64) (*User, error) {
 	var u User