feat(PROJ-28): FQDN + smtp_out Konfiguration

- config: server.fqdn, SMTPOutConfig, smtp_out Abschnitt
- config: IMAPServerConfig.FQDN (runtime-gesetzt)
- main: FQDN-Fallback für SMTP EHLO, FQDN an IMAP-Server
- imapserver: Greeting nutzt server.fqdn (RFC 3501)
- smtpd/imapserver Modulversion 1.3

fix: Superadmin sieht keine Suche/IMAP/POP3 Nav-Links

- Navbar: Suche, IMAP Import, POP3 Import nur für non-superadmin
- Superadmin landet direkt auf Admin-Dashboard

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/config.go

@@ -25,6 +25,7 @@ type Config struct {
 	Storage    StorageConfig    `yaml:"storage"`
 	Database   DatabaseConfig   `yaml:"database"`
 	SMTP       SMTPConfig       `yaml:"smtp"`
+	SMTPOut    SMTPOutConfig    `yaml:"smtp_out"`
 	API        APIConfig        `yaml:"api"`
 	Index      IndexConfig      `yaml:"index"`
 	Audit      AuditConfig      `yaml:"audit"`
@@ -35,15 +36,27 @@ type Config struct {
 // IMAPServerConfig holds settings for the embedded read-only IMAP archive server.
 type IMAPServerConfig struct {
 	Enabled bool   `yaml:"enabled"`
-	Bind    string `yaml:"bind"`    // plain: ":1143", TLS: ":993"
+	Bind    string `yaml:"bind"`     // plain: ":1143", TLS: ":993"
 	TLSCert string `yaml:"tls_cert"` // path to PEM certificate; if set, TLS is enabled
 	TLSKey  string `yaml:"tls_key"`  // path to PEM private key
+	FQDN    string `yaml:"-"`        // set at runtime from server.fqdn
 }
 
 // ServerConfig holds port settings for the main services.
 type ServerConfig struct {
-	APIPort  int `yaml:"api_port"`
-	SMTPPort int `yaml:"smtp_port"`
+	FQDN     string `yaml:"fqdn"`      // Fully Qualified Domain Name — used in SMTP EHLO, IMAP greeting, and generated links
+	APIPort  int    `yaml:"api_port"`
+	SMTPPort int    `yaml:"smtp_port"`
+}
+
+// SMTPOutConfig holds settings for outgoing email (password reset, invitations).
+type SMTPOutConfig struct {
+	Host     string `yaml:"host"`
+	Port     int    `yaml:"port"`
+	User     string `yaml:"user"`
+	Password string `yaml:"password"`
+	TLS      bool   `yaml:"tls"`
+	From     string `yaml:"from"` // e.g. "archivmail <noreply@firma.de>"
 }
 
 // StorageConfig holds file system paths for email storage.