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/oauth.go

@@ -119,7 +119,7 @@ type OidcUser struct {
 
 func (ou *OidcUser) ToOauthUser() *OauthUser {
 	var username string
-	// 使用 PreferredUsername，如果不存在，降级到 Email 前缀
+	// Use PreferredUsername; if not present, fall back to the Email prefix
 	if ou.PreferredUsername != "" {
 		username = ou.PreferredUsername
 	} else {
@@ -169,7 +169,7 @@ func (lu *LinuxdoUser) ToOauthUser() *OauthUser {
 		Name:          lu.Name,
 		Username:      strings.ToLower(lu.Username),
 		Email:         lu.Email,
-		VerifiedEmail: true, // linux.do 用户邮箱默认已验证
+		VerifiedEmail: true, // linux.do user emails are verified by default
 		Picture:       lu.Avatar,
 	}
 }