Fix widget i18n missing locale files and clean up unused locales

- widget/i18n/index.js: only import en.json and zh_CN.json (the only
  locale files present); remove 40+ imports for missing locale JSONs
  that caused Vite compile failure and global white screen
- dashboard/i18n/index.js: remove unused locale imports for consistency
- Remove 62 unused locale JSON files from widget/i18n/locale/
- Minor: update index.html, test helpers, e2e test, languages spec

backend/cmd/gochat/main.go

@@ -136,7 +136,7 @@ func seedSmokeData(ctx context.Context, db *gorm.DB) (*smokeSeedSummary, error)
 
 	account := &model.Account{}
 	smokeFeatureFlags := `{"advanced_assignment":true,"assignment_v2":true,"audit_logs":true,"automations":true,"captain_integration":true,"captain_integration_v2":true,"captain_tasks":true,"companies":true,"crm":true,"csat":true,"custom_roles":true,"custom_tools":true,"inbox_management":true,"macros":true,"reports":true,"sla":true}`
-	if err := db.WithContext(ctx).Where("name = ?", accountName).FirstOrCreate(account, model.Account{Name: accountName, Locale: "en", Timezone: "UTC", Active: true, Status: "active", FeatureFlags: smokeFeatureFlags}).Error; err != nil {
+	if err := db.WithContext(ctx).Where("name = ?", accountName).FirstOrCreate(account, model.Account{Name: accountName, Locale: "zh_CN", Timezone: "UTC", Active: true, Status: "active", FeatureFlags: smokeFeatureFlags}).Error; err != nil {
 		return nil, fmt.Errorf("seed account: %w", err)
 	}
 	if err := db.WithContext(ctx).Model(account).Updates(map[string]any{"active": true, "status": "active", "feature_flags": smokeFeatureFlags}).Error; err != nil {

backend/internal/model/account.go

@@ -11,7 +11,7 @@ type Account struct {
 	Base
 	Name                string         `gorm:"size:255;not null" json:"name"`
 	Domain              string         `gorm:"size:255" json:"domain,omitempty"`
-	Locale              string         `gorm:"size:10;default:en" json:"locale"`
+	Locale              string         `gorm:"size:10;default:zh_CN" json:"locale"`
 	Timezone            string         `gorm:"size:50;default:UTC" json:"timezone"`
 	ReportingTimezone   string         `gorm:"size:100" json:"reporting_timezone,omitempty"`
 	Active              bool           `gorm:"default:true" json:"active"`

backend/pkg/testutil/fixtures.go

@@ -17,7 +17,7 @@ import (
 func NewAccountFixture(name string) *model.Account {
 	return &model.Account{
 		Name:     name,
-		Locale:   "en",
+		Locale:   "zh_CN",
 		Timezone: "UTC",
 		Active:   true,
 	}

backend/pkg/testutil/helpers.go

@@ -166,7 +166,7 @@ func AssertTimestampOrder(t *testing.T, createdAt, updatedAt time.Time) {
 // SeedAccount creates and persists a test account.
 func SeedAccount(t *testing.T, db *gorm.DB, name string) *model.Account {
 	t.Helper()
-	acc := &model.Account{Name: name, Locale: "en", Timezone: "UTC", Active: true}
+	acc := &model.Account{Name: name, Locale: "zh_CN", Timezone: "UTC", Active: true}
 	err := db.Create(acc).Error
 	assert.NoError(t, err, "failed to seed account")
 	return acc

backend/tests/e2e/e2e_test.go

@@ -242,7 +242,7 @@ func (s *E2ETestSuite) Router() *gin.Engine {
 func (s *E2ETestSuite) CreateTestAccount(name string) *model.Account {
 	account := &model.Account{
 		Name:     name,
-		Locale:   "en",
+		Locale:   "zh_CN",
 		Timezone: "UTC",
 		Active:   true,
 	}