fix: address load_factor code review findings

- Fix bulk edit: send 0 instead of null/NaN to clear load_factor
- Fix edit modal: explicit NaN check instead of implicit falsy
- Fix create modal: use ?? instead of || for load_factor
- Add load_factor upper limit validation (max 10000)
- Add //go:build unit tag and self-contained intPtrHelper in test
- Add design intent comments on WaitPlan.MaxConcurrency

backend/internal/service/account_load_factor_test.go

@@ -1,3 +1,5 @@
+//go:build unit
+
 package service
 
 import (
@@ -6,6 +8,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func intPtrHelper(v int) *int { return &v }
+
 func TestEffectiveLoadFactor_NilAccount(t *testing.T) {
 	var a *Account
 	require.Equal(t, 1, a.EffectiveLoadFactor())
@@ -22,21 +26,21 @@ func TestEffectiveLoadFactor_NilLoadFactor_ZeroConcurrency(t *testing.T) {
 }
 
 func TestEffectiveLoadFactor_PositiveLoadFactor(t *testing.T) {
-	a := &Account{Concurrency: 5, LoadFactor: intPtr(20)}
+	a := &Account{Concurrency: 5, LoadFactor: intPtrHelper(20)}
 	require.Equal(t, 20, a.EffectiveLoadFactor())
 }
 
 func TestEffectiveLoadFactor_ZeroLoadFactor_FallbackToConcurrency(t *testing.T) {
-	a := &Account{Concurrency: 5, LoadFactor: intPtr(0)}
+	a := &Account{Concurrency: 5, LoadFactor: intPtrHelper(0)}
 	require.Equal(t, 5, a.EffectiveLoadFactor())
 }
 
 func TestEffectiveLoadFactor_NegativeLoadFactor_FallbackToConcurrency(t *testing.T) {
-	a := &Account{Concurrency: 3, LoadFactor: intPtr(-1)}
+	a := &Account{Concurrency: 3, LoadFactor: intPtrHelper(-1)}
 	require.Equal(t, 3, a.EffectiveLoadFactor())
 }
 
 func TestEffectiveLoadFactor_ZeroLoadFactor_ZeroConcurrency(t *testing.T) {
-	a := &Account{Concurrency: 0, LoadFactor: intPtr(0)}
+	a := &Account{Concurrency: 0, LoadFactor: intPtrHelper(0)}
 	require.Equal(t, 1, a.EffectiveLoadFactor())
 }

backend/internal/service/admin_service.go

@@ -1417,6 +1417,9 @@ func (s *adminServiceImpl) CreateAccount(ctx context.Context, input *CreateAccou
 		account.RateMultiplier = input.RateMultiplier
 	}
 	if input.LoadFactor != nil && *input.LoadFactor > 0 {
+		if *input.LoadFactor > 10000 {
+			return nil, errors.New("load_factor must be <= 10000")
+		}
 		account.LoadFactor = input.LoadFactor
 	}
 	if err := s.accountRepo.Create(ctx, account); err != nil {
@@ -1492,6 +1495,8 @@ func (s *adminServiceImpl) UpdateAccount(ctx context.Context, id int64, input *U
 	if input.LoadFactor != nil {
 		if *input.LoadFactor <= 0 {
 			account.LoadFactor = nil // 0 或负数表示清除
+		} else if *input.LoadFactor > 10000 {
+			return nil, errors.New("load_factor must be <= 10000")
 		} else {
 			account.LoadFactor = input.LoadFactor
 		}

backend/internal/service/openai_account_scheduler.go

@@ -342,6 +342,7 @@ func (s *defaultOpenAIAccountScheduler) selectBySessionHash(
 	}
 
 	cfg := s.service.schedulingConfig()
+	// WaitPlan.MaxConcurrency 使用 Concurrency（非 EffectiveLoadFactor），因为 WaitPlan 控制的是 Redis 实际并发槽位等待。
 	if s.service.concurrencyService != nil {
 		return &AccountSelectionResult{
 			Account: account,
@@ -703,6 +704,7 @@ func (s *defaultOpenAIAccountScheduler) selectByLoadBalance(
 	}
 
 	cfg := s.service.schedulingConfig()
+	// WaitPlan.MaxConcurrency 使用 Concurrency（非 EffectiveLoadFactor），因为 WaitPlan 控制的是 Redis 实际并发槽位等待。
 	candidate := selectionOrder[0]
 	return &AccountSelectionResult{
 		Account: candidate.account,