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>

frontend/src/lib/types.ts

@@ -203,6 +203,7 @@ export interface SystemSettings {
   smtpPass?: string; // write only: the server never sends it back, empty keeps the stored one
   smtpPassSet?: boolean;
   smtpFrom?: string;
+  smtpFromName?: string; // display name when smtpFrom is a bare address (empty = MindSift)
   smtpTls?: boolean;
   smtpSkipVerify?: boolean;
   allowPrivateWebhooks?: boolean; // alarm webhooks may reach the LAN (and plain http)