fix(admin): SMTP port can be cleared and saves without 'Ungültiges JSON'

The UI sent the port as a number while the server expects text, so every
save failed; the field also jumped back to 587 when emptied. The port is
now edited as text (digits only), and the server accepts number or text.

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

frontend/src/features/settings/AdminSettingsView.tsx

@@ -96,7 +96,7 @@ export const AdminSettingsView: React.FC<AdminSettingsViewProps> = ({
     allowRegistration: false,
     instanceName: 'MindSift',
     smtpHost: '',
-    smtpPort: 587,
+    smtpPort: '587',
     smtpUser: '',
     smtpPass: '',
     smtpFrom: '',
@@ -126,7 +126,7 @@ export const AdminSettingsView: React.FC<AdminSettingsViewProps> = ({
           allowRegistration: Boolean(sys.allowRegistration),
           instanceName: sys.instanceName || 'MindSift',
           smtpHost: sys.smtpHost || '',
-          smtpPort: sys.smtpPort || 587,
+          smtpPort: sys.smtpPort ? String(sys.smtpPort) : '587',
           smtpUser: sys.smtpUser || '',
           smtpPass: sys.smtpPass || '',
           smtpFrom: sys.smtpFrom || '',
@@ -1150,10 +1150,12 @@ export const AdminSettingsView: React.FC<AdminSettingsViewProps> = ({
                     SMTP Port (`SMTP_PORT`)
                   </label>
                   <input
-                    type="number"
-                    value={settings.smtpPort || 587}
+                    type="text"
+                    inputMode="numeric"
+                    value={settings.smtpPort ?? ''}
                     onChange={(e) =>
-                      setSettings((prev) => ({ ...prev, smtpPort: Number(e.target.value) }))
+                      // Digits only; an empty field stays empty while typing (saved as 587)
+                      setSettings((prev) => ({ ...prev, smtpPort: e.target.value.replace(/\D/g, '').slice(0, 5) }))
                     }
                     placeholder="587"
                     className="w-full h-9 px-3 input-field font-mono"

frontend/src/lib/types.ts

@@ -161,7 +161,7 @@ export interface SystemSettings {
   allowRegistration: boolean;
   instanceName: string;
   smtpHost?: string;
-  smtpPort?: number;
+  smtpPort?: string; // sent as text, like the server stores it
   smtpUser?: string;
   smtpPass?: string;
   smtpFrom?: string;

internal/domain/models.go

@@ -3,6 +3,7 @@ package domain
 import (
 	"crypto/rand"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strings"
@@ -289,6 +290,36 @@ type SystemSettings struct {
 	SMTPConfiguredViaEnv bool   `json:"smtpConfiguredViaEnv,omitempty"`
 }
 
+// UnmarshalJSON accepts smtpPort as text or number: older clients sent a number, which made the whole
+// settings request fail with "Ungültiges JSON".
+func (s *SystemSettings) UnmarshalJSON(data []byte) error {
+	type plain SystemSettings
+	aux := struct {
+		*plain
+		SMTPPort json.RawMessage `json:"smtpPort"`
+	}{plain: (*plain)(s)}
+	if err := json.Unmarshal(data, &aux); err != nil {
+		return err
+	}
+	port := strings.TrimSpace(string(aux.SMTPPort))
+	switch {
+	case port == "" || port == "null":
+	case strings.HasPrefix(port, `"`):
+		var str string
+		if err := json.Unmarshal(aux.SMTPPort, &str); err != nil {
+			return err
+		}
+		s.SMTPPort = strings.TrimSpace(str)
+	default:
+		var n json.Number
+		if err := json.Unmarshal(aux.SMTPPort, &n); err != nil {
+			return err
+		}
+		s.SMTPPort = n.String()
+	}
+	return nil
+}
+
 type DocumentBlock struct {
 	ID         string  `json:"id"`
 	DocumentID string  `json:"documentId,omitempty"`

internal/domain/tags_test.go

@@ -1,6 +1,7 @@
 package domain
 
 import (
+	"encoding/json"
 	"reflect"
 	"testing"
 )
@@ -32,3 +33,19 @@ func TestStaleAnchorTags(t *testing.T) {
 		t.Fatalf("only tags that exist solely as anchors are stale, got %v", got)
 	}
 }
+
+func TestSystemSettingsAcceptsPortAsNumberOrText(t *testing.T) {
+	for _, body := range []string{`{"smtpPort": 465, "smtpHost": "mail"}`, `{"smtpPort": "465", "smtpHost": "mail"}`} {
+		var s SystemSettings
+		if err := json.Unmarshal([]byte(body), &s); err != nil {
+			t.Fatalf("%s: %v", body, err)
+		}
+		if s.SMTPPort != "465" || s.SMTPHost != "mail" {
+			t.Errorf("%s: got port %q host %q", body, s.SMTPPort, s.SMTPHost)
+		}
+	}
+	var empty SystemSettings
+	if err := json.Unmarshal([]byte(`{"smtpPort": ""}`), &empty); err != nil || empty.SMTPPort != "" {
+		t.Errorf("empty port: %q (%v)", empty.SMTPPort, err)
+	}
+}