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/user.go

@@ -7,7 +7,7 @@ import (
 type UserForm struct {
 	Id       uint   `json:"id"`
 	Username string `json:"username" validate:"required,gte=2,lte=32"`
-	Email    string `json:"email"` //validate:"required,email" email不强制
+	Email    string `json:"email"` //validate:"required,email" emailnot enforced
 	//Password string           `json:"password" validate:"required,gte=4,lte=20"`
 	Nickname string           `json:"nickname"`
 	Avatar   string           `json:"avatar"`