Add portainer bootstrap compose to repo

Mirrors the live /mnt/containers/portainer/docker-compose.yaml on serverweb,
previously only on the host.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

portainer/docker-compose.yaml

@@ -0,0 +1,11 @@
+services:
+    portainer:
+      image: portainer/portainer-ce:latest
+      container_name: portainer
+      restart: always
+      privileged: true
+      volumes:
+        - /mnt/containers/portainer/container-data/data:/data:Z
+        - /var/run/docker.sock:/var/run/docker.sock:Z
+      ports:
+        - 9443:9443