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/storage/system.go

@@ -92,7 +92,7 @@ func (s *Store) ExportUserData(userID string) (*domain.FullExport, error) {
 
 // --- SYSTEM SETTINGS ---
 
-func (s *Store) SeedSMTPDefaultsFromEnv(host, port, user, pass, from string, tls, skipVerify bool) {
+func (s *Store) SeedSMTPDefaultsFromEnv(host, port, user, pass, from, fromName string, tls, skipVerify bool) {
 	cur, err := s.GetSystemSettings()
 	if err != nil || cur == nil {
 		return
@@ -106,6 +106,7 @@ func (s *Store) SeedSMTPDefaultsFromEnv(host, port, user, pass, from string, tls
 		cur.SMTPUser = strings.TrimSpace(user)
 		cur.SMTPPass = pass
 		cur.SMTPFrom = strings.TrimSpace(from)
+		cur.SMTPFromName = strings.TrimSpace(fromName)
 		cur.SMTPTLS = tls
 		cur.SMTPSkipVerify = skipVerify
 		_ = s.UpdateSystemSettings(cur)
@@ -151,6 +152,8 @@ func (s *Store) GetSystemSettings() (*domain.SystemSettings, error) {
 				settings.SMTPPass = v
 			case "smtp_from":
 				settings.SMTPFrom = v
+			case "smtp_from_name":
+				settings.SMTPFromName = v
 			case "smtp_tls":
 				settings.SMTPTLS = (v != "false" && v != "0")
 			case "smtp_skip_verify":
@@ -212,6 +215,7 @@ func (s *Store) UpdateSystemSettings(settings *domain.SystemSettings) error {
 		('smtp_user', ?),
 		('smtp_pass', ?),
 		('smtp_from', ?),
+		('smtp_from_name', ?),
 		('smtp_tls', ?),
 		('smtp_skip_verify', ?),
 		('allow_private_webhooks', ?),
@@ -227,6 +231,7 @@ func (s *Store) UpdateSystemSettings(settings *domain.SystemSettings) error {
 		strings.TrimSpace(settings.SMTPUser),
 		settings.SMTPPass,
 		strings.TrimSpace(settings.SMTPFrom),
+		strings.TrimSpace(settings.SMTPFromName),
 		tlsStr,
 		skipVerifyStr,
 		privateHooksStr,