fix: add 6 missing apps to first-boot and fix penpot icon path

Added searxng, onlyoffice, filebrowser, nginx-proxy-manager, portainer,
and tailscale to first-boot-containers.sh so fresh ISO installs have all
marketplace apps ready. Fixed penpot icon path in Marketplace.vue to use
the correct app-icons directory.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/src/views/Marketplace.vue

@@ -653,7 +653,7 @@ function getCuratedAppList() {
       title: 'Penpot',
       version: '2.0.0',
       description: 'Open-source design and prototyping platform. Self-hosted alternative to Figma.',
-      icon: '/assets/img/penpot.webp',
+      icon: '/assets/img/app-icons/penpot.webp',
       author: 'Penpot',
       dockerImage: 'docker.io/penpotapp/frontend:latest',
       manifestUrl: null,