fix: add MAIL_FROM env (default mgmt@msbls.de) + graceful fallback when m CLI unavailable

backend/internal/services/notification_service.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"os"
 	"os/exec"
 	"strings"
 	"sync"
@@ -458,17 +459,25 @@ type UpdatePreferencesInput struct {
 }
 
 // SendEmail sends an email using the `m mail send` CLI command.
+// In Docker, this will fail gracefully (m CLI not available).
+// TODO: Replace with direct SMTP for production.
 func SendEmail(to, subject, body string) error {
+	from := os.Getenv("MAIL_FROM")
+	if from == "" {
+		from = "mgmt@msbls.de"
+	}
 	cmd := exec.Command("m", "mail", "send",
+		"--from", from,
 		"--to", to,
 		"--subject", subject,
 		"--body", body,
 		"--yes")
 	output, err := cmd.CombinedOutput()
 	if err != nil {
-		return fmt.Errorf("m mail send failed: %w (output: %s)", err, string(output))
+		slog.Warn("email send failed (m CLI may not be available in Docker)", "to", to, "error", err, "output", string(output))
+		return fmt.Errorf("m mail send failed: %w", err)
 	}
-	slog.Info("email sent", "to", to, "subject", subject)
+	slog.Info("email sent", "from", from, "to", to, "subject", subject)
 	return nil
 }