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/domain/models.go

@@ -287,9 +287,11 @@ type SystemSettings struct {
 	SMTPUser          string `json:"smtpUser"`
 	// SMTPPass is never sent to the browser (FLAW-34): reads leave it empty and set SMTPPassSet;
 	// writing it empty keeps the stored password
-	SMTPPass       string `json:"smtpPass"`
-	SMTPPassSet    bool   `json:"smtpPassSet,omitempty"`
-	SMTPFrom       string `json:"smtpFrom"`
+	SMTPPass    string `json:"smtpPass"`
+	SMTPPassSet bool   `json:"smtpPassSet,omitempty"`
+	SMTPFrom    string `json:"smtpFrom"`
+	// SMTPFromName is shown as sender when SMTPFrom is a bare address (empty = "MindSift")
+	SMTPFromName   string `json:"smtpFromName"`
 	SMTPTLS        bool   `json:"smtpTls"`
 	SMTPSkipVerify bool   `json:"smtpSkipVerify"` // accept self-signed certificates
 	// AllowPrivateWebhooks lets alarm webhooks reach LAN addresses (and plain http); localhost and cloud