feat: 重构配置文件格式并添加 IMAP ID 命令支持

- 配置文件分离：用户配置与项目配置分离，项目级配置（客户端信息、需要 ID 命令的 provider）放在代码中
- 新增 check_id 字段：用户可选择禁用单个账户的 ID 命令发送
- 简化 provider：只保留 163 和 QQ，移除未使用的 Gmail/Outlook/188 等
- 修复 163 邮箱收件箱问题：通过发送 IMAP ID 命令解决 Unsafe Login 错误

BREAKING CHANGE: 配置文件格式变化，旧配置不兼容

main.go

@@ -203,6 +203,7 @@ func init() {
 	rootCmd.AddCommand(ManCmd)
 
 	cfg, _ := loadConfig()
+	_ = cfg
 
 	rootCmd.Flags().StringSliceVar(&bcc, "bcc", []string{}, "BCC recipients")
 	rootCmd.Flags().StringSliceVar(&cc, "cc", []string{}, "CC recipients")
@@ -211,7 +212,7 @@ func init() {
 	rootCmd.Flags().StringVarP(&body, "body", "b", "", "Email's contents")
 	envFrom := os.Getenv(PopFrom)
 	if envFrom == "" {
-		envFrom = cfg.From
+		envFrom = getDefaultFromEmail()
 	}
 	from = envFrom
 	rootCmd.Flags().StringVarP(&from, "from", "f", envFrom, "Email's sender"+commentStyle.Render("($"+PopFrom+")"))
@@ -228,46 +229,52 @@ func init() {
 	}
 	rootCmd.Flags().StringVarP(&signature, "signature", "x", envSignature, "Signature to display at the end of the email."+commentStyle.Render("($"+PopSignature+")"))
 	envSMTPHost := os.Getenv(PopSMTPHost)
-	if envSMTPHost == "" {
-		envSMTPHost = cfg.SMTP.Host
-	}
-	smtpHost = envSMTPHost
-	rootCmd.Flags().StringVarP(&smtpHost, "smtp.host", "H", envSMTPHost, "Host of the SMTP server"+commentStyle.Render("($"+PopSMTPHost+")"))
 	envSMTPPort, _ := strconv.Atoi(os.Getenv(PopSMTPPort))
-	if envSMTPPort == 0 {
-		envSMTPPort = cfg.SMTP.Port
+	envSMTPUsername := os.Getenv(PopSMTPUsername)
+	envSMTPPassword := os.Getenv(PopSMTPPassword)
+	envSMTPEncryption := os.Getenv(PopSMTPEncryption)
+	envInsecureSkipVerify := os.Getenv(PopSMTPInsecureSkipVerify) == "true"
+
+	defaultAccounts, _ := getAccounts()
+	defaultAccount := getDefaultAccount(defaultAccounts, cfg.From.Account)
+
+	if envSMTPHost == "" && defaultAccount != nil {
+		envSMTPHost = defaultAccount.SMTP.Host
+	}
+	if envSMTPPort == 0 && defaultAccount != nil {
+		envSMTPPort = defaultAccount.SMTP.Port
 		if envSMTPPort == 0 {
 			envSMTPPort = 587
 		}
 	}
-	smtpPort = envSMTPPort
-	rootCmd.Flags().IntVarP(&smtpPort, "smtp.port", "P", envSMTPPort, "Port of the SMTP server"+commentStyle.Render("($"+PopSMTPPort+")"))
-	envSMTPUsername := os.Getenv(PopSMTPUsername)
-	if envSMTPUsername == "" {
-		envSMTPUsername = cfg.SMTP.Username
+	if envSMTPUsername == "" && defaultAccount != nil {
+		envSMTPUsername = defaultAccount.SMTP.Username
 	}
-	smtpUsername = envSMTPUsername
-	rootCmd.Flags().StringVarP(&smtpUsername, "smtp.username", "U", envSMTPUsername, "Username of the SMTP server"+commentStyle.Render("($"+PopSMTPUsername+")"))
-	envSMTPPassword := os.Getenv(PopSMTPPassword)
-	if envSMTPPassword == "" {
-		envSMTPPassword = cfg.SMTP.Password
+	if envSMTPPassword == "" && defaultAccount != nil {
+		envSMTPPassword = defaultAccount.SMTP.Password
 	}
-	smtpPassword = envSMTPPassword
-	rootCmd.Flags().StringVarP(&smtpPassword, "smtp.password", "p", envSMTPPassword, "Password of the SMTP server"+commentStyle.Render("($"+PopSMTPPassword+")"))
-	envSMTPEncryption := os.Getenv(PopSMTPEncryption)
-	if envSMTPEncryption == "" {
-		envSMTPEncryption = cfg.SMTP.Encryption
+	if envSMTPEncryption == "" && defaultAccount != nil {
+		envSMTPEncryption = defaultAccount.SMTP.Encryption
 		if envSMTPEncryption == "" {
 			envSMTPEncryption = "starttls"
 		}
 	}
-	smtpEncryption = envSMTPEncryption
-	rootCmd.Flags().StringVarP(&smtpEncryption, "smtp.encryption", "e", envSMTPEncryption, "Encryption type of the SMTP server (starttls, ssl, or none)"+commentStyle.Render("($"+PopSMTPEncryption+")"))
-	envInsecureSkipVerify := os.Getenv(PopSMTPInsecureSkipVerify) == "true"
-	if !envInsecureSkipVerify {
-		envInsecureSkipVerify = cfg.SMTP.InsecureSkipVerify
+	if !envInsecureSkipVerify && defaultAccount != nil {
+		envInsecureSkipVerify = defaultAccount.SMTP.InsecureSkipVerify
 	}
+
+	smtpHost = envSMTPHost
+	smtpPort = envSMTPPort
+	smtpUsername = envSMTPUsername
+	smtpPassword = envSMTPPassword
+	smtpEncryption = envSMTPEncryption
 	smtpInsecureSkipVerify = envInsecureSkipVerify
+
+	rootCmd.Flags().StringVarP(&smtpHost, "smtp.host", "H", envSMTPHost, "Host of the SMTP server"+commentStyle.Render("($"+PopSMTPHost+")"))
+	rootCmd.Flags().IntVarP(&smtpPort, "smtp.port", "P", envSMTPPort, "Port of the SMTP server"+commentStyle.Render("($"+PopSMTPPort+")"))
+	rootCmd.Flags().StringVarP(&smtpUsername, "smtp.username", "U", envSMTPUsername, "Username of the SMTP server"+commentStyle.Render("($"+PopSMTPUsername+")"))
+	rootCmd.Flags().StringVarP(&smtpPassword, "smtp.password", "p", envSMTPPassword, "Password of the SMTP server"+commentStyle.Render("($"+PopSMTPPassword+")"))
+	rootCmd.Flags().StringVarP(&smtpEncryption, "smtp.encryption", "e", envSMTPEncryption, "Encryption type of the SMTP server (starttls, ssl, or none)"+commentStyle.Render("($"+PopSMTPEncryption+")"))
 	rootCmd.Flags().BoolVarP(&smtpInsecureSkipVerify, "smtp.insecure", "i", envInsecureSkipVerify, "Skip TLS verification with SMTP server"+commentStyle.Render("($"+PopSMTPInsecureSkipVerify+")"))
 	envResendAPIKey := os.Getenv(ResendAPIKey)
 	rootCmd.Flags().StringVarP(&resendAPIKey, "resend.key", "r", envResendAPIKey, "API key for the Resend.com"+commentStyle.Render("($"+ResendAPIKey+")"))