i18n: Translate all Chinese to English across the codebase

Translate Chinese comments, log/error messages, validator labels and
Swagger annotations to English throughout the source code, generated
Swagger docs, config files and CI workflows.

Make the English README primary: README.md now holds the English docs
and README_EN.md holds the Chinese version, with cross-language links
updated accordingly.

Note: the generated docs/ swagger files were translated in place; run
`go generate ./...` (swag init) to regenerate them from the now-English
annotations when a Go toolchain is available.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

model/user.go

@@ -15,9 +15,9 @@ type User struct {
 	TimeModel
 }
 
-// BeforeSave 钩子用于确保 email 字段有合理的默认值
+// BeforeSave hook ensures the email field has a sensible default value
 //func (u *User) BeforeSave(tx *gorm.DB) (err error) {
-//	// 如果 email 为空，设置为默认值
+//	// If email is empty, set it to a default value
 //	if u.Email == "" {
 //		u.Email = fmt.Sprintf("%s@example.com", u.Username)
 //	}