fix(payment): return decrypted non-sensitive config on provider list

- Backend: add ListProviderInstancesWithConfig that decrypts config
  and masks sensitive fields (keys, secrets) as "••••••••"
- Frontend: pre-fill non-sensitive config values when editing provider
  (PID, API base URL, notify URL, return URL, channel IDs etc.)
- Sensitive fields left empty for user to re-enter if needed

backend/internal/handler/admin/payment_handler.go

@@ -221,7 +221,7 @@ func (h *PaymentHandler) DeletePlan(c *gin.Context) {
 // ListProviders returns all payment provider instances.
 // GET /api/v1/admin/payment/providers
 func (h *PaymentHandler) ListProviders(c *gin.Context) {
-	providers, err := h.configService.ListProviderInstances(c.Request.Context())
+	providers, err := h.configService.ListProviderInstancesWithConfig(c.Request.Context())
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return

backend/internal/service/payment_config_service.go

@@ -244,6 +244,64 @@ func (s *PaymentConfigService) ListProviderInstances(ctx context.Context) ([]*db
 	return s.entClient.PaymentProviderInstance.Query().Order(paymentproviderinstance.BySortOrder()).All(ctx)
 }
 
+// ProviderInstanceResponse is the API response for a provider instance.
+// Config contains non-sensitive fields in cleartext; sensitive fields are masked.
+type ProviderInstanceResponse struct {
+	ID             int64             `json:"id"`
+	ProviderKey    string            `json:"provider_key"`
+	Name           string            `json:"name"`
+	Config         map[string]string `json:"config"`
+	SupportedTypes string            `json:"supported_types"`
+	Limits         string            `json:"limits"`
+	Enabled        bool              `json:"enabled"`
+	RefundEnabled  bool              `json:"refund_enabled"`
+	SortOrder      int               `json:"sort_order"`
+}
+
+// ListProviderInstancesWithConfig returns provider instances with decrypted
+// non-sensitive config fields and masked sensitive fields.
+func (s *PaymentConfigService) ListProviderInstancesWithConfig(ctx context.Context) ([]ProviderInstanceResponse, error) {
+	instances, err := s.entClient.PaymentProviderInstance.Query().
+		Order(paymentproviderinstance.BySortOrder()).All(ctx)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]ProviderInstanceResponse, 0, len(instances))
+	for _, inst := range instances {
+		resp := ProviderInstanceResponse{
+			ID: int64(inst.ID), ProviderKey: inst.ProviderKey, Name: inst.Name,
+			SupportedTypes: inst.SupportedTypes, Limits: inst.Limits,
+			Enabled: inst.Enabled, RefundEnabled: inst.RefundEnabled, SortOrder: inst.SortOrder,
+		}
+		resp.Config = s.decryptAndMaskConfig(inst.Config)
+		result = append(result, resp)
+	}
+	return result, nil
+}
+
+func (s *PaymentConfigService) decryptAndMaskConfig(encrypted string) map[string]string {
+	if encrypted == "" {
+		return nil
+	}
+	decrypted, err := payment.Decrypt(encrypted, s.encryptionKey)
+	if err != nil {
+		return nil
+	}
+	var raw map[string]string
+	if err := json.Unmarshal([]byte(decrypted), &raw); err != nil {
+		return nil
+	}
+	masked := make(map[string]string, len(raw))
+	for k, v := range raw {
+		if isSensitiveConfigField(k) && v != "" {
+			masked[k] = "••••••••"
+		} else {
+			masked[k] = v
+		}
+	}
+	return masked
+}
+
 // pendingOrderStatuses are order statuses considered "in progress" —
 // modifying provider credentials or deleting a provider/plan is blocked
 // while orders in these states exist.

frontend/src/components/payment/PaymentProviderDialog.vue

@@ -349,6 +349,15 @@ function loadProvider(provider: ProviderInstance) {
   form.enabled = provider.enabled
   form.refund_enabled = provider.refund_enabled
   clearConfig()
+  // Pre-fill config from API response (non-sensitive in cleartext, sensitive masked)
+  if (provider.config) {
+    for (const [k, v] of Object.entries(provider.config)) {
+      // Skip masked sensitive values — leave field empty so user can re-enter
+      if (v !== '••••••••') {
+        config[k] = v
+      }
+    }
+  }
   // Parse existing limits
   if (provider.limits) {
     try {

frontend/src/types/payment.ts

@@ -103,6 +103,7 @@ export interface ProviderInstance {
   id: number
   provider_key: string
   name: string
+  config: Record<string, string>
   supported_types: string
   enabled: boolean
   refund_enabled: boolean