feat(mail): sender display name (SMTP_FROM_NAME, default MindSift)

A bare SMTP_FROM address gets the display name in the From header; a name
already in SMTP_FROM wins, the envelope keeps the bare address. Also a
field in the admin mail settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/config/config.go

@@ -37,7 +37,9 @@ type Config struct {
 	SMTPUser string
 	SMTPPass string
 	SMTPFrom string
-	SMTPTLS  bool
+	// SMTPFromName is the sender's display name when SMTP_FROM is a bare address
+	SMTPFromName string
+	SMTPTLS      bool
 	// SMTPSkipVerify accepts self-signed or mismatching certificates (internal mail servers)
 	SMTPSkipVerify bool
 
@@ -220,6 +222,7 @@ func Load() *Config {
 		SMTPUser:               smtpUser,
 		SMTPPass:               smtpPass,
 		SMTPFrom:               smtpFrom,
+		SMTPFromName:           getEnv("SMTP_FROM_NAME", "MindSift"),
 		SMTPTLS:                smtpTLS,
 		SMTPSkipVerify:         smtpSkipVerify,
 		Speech: SpeechConfig{