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>

http/request/admin/login.go

@@ -1,10 +1,10 @@
 package admin
 
 type Login struct {
-	Username  string `json:"username" validate:"required" label:"用户名"`
-	Password  string `json:"password,omitempty" validate:"required" label:"密码"`
-	Platform  string `json:"platform" label:"平台"`
-	Captcha   string `json:"captcha,omitempty" label:"验证码"`
+	Username  string `json:"username" validate:"required" label:"username"`
+	Password  string `json:"password,omitempty" validate:"required" label:"password"`
+	Platform  string `json:"platform" label:"platform"`
+	Captcha   string `json:"captcha,omitempty" label:"captcha"`
 	CaptchaId string `json:"captcha_id,omitempty"`
 }