feat: add device deletion endpoint with cascade cleanup and admin UI integration

Add DELETE /admin/devices/{id} endpoint with cascade deletion of device records, WireGuard peers, IP allocations, and device access profile settings. Update device status to 'deleted' and set deleted_at timestamp while preserving revoked_at if already set.

Add deleteDevice API method and delete button to devices page with query invalidation for both devices and device-profile lists. Record admin.device.deleted audit

backend/internal/device/service.go

@@ -189,6 +189,10 @@ func (s *Service) Revoke(ctx context.Context, deviceID uuid.UUID) error {
 	return s.repo.Revoke(ctx, deviceID)
 }
 
+func (s *Service) Delete(ctx context.Context, deviceID uuid.UUID) error {
+	return s.repo.Delete(ctx, deviceID)
+}
+
 func (s *Service) Rotate(ctx context.Context, deviceID uuid.UUID) error {
 	return s.repo.Rotate(ctx, deviceID)
 }