chore(relocate): stub out S1 items moved to railiance-infra

cloudinit/user-data.yaml and tools/cmd/railiance-plan-host relocated
to railiance-infra per ADR-003. Tombstone stubs left in place.

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

cloudinit/user-data.yaml

@@ -1,12 +1,2 @@
-#cloud-config
-package_update: true
-package_upgrade: true
-users:
-  - name: ubuntu
-    sudo: ALL=(ALL) NOPASSWD:ALL
-    groups: sudo
-    shell: /bin/bash
-    ssh_authorized_keys:
-      - ssh-ed25519 AAAA...replace_with_your_pubkey
-runcmd:
-  - [ sh, -lc, 'echo Railiance seed host initialized' ]
+# RELOCATED — this file has moved to railiance-infra/cloudinit/user-data.yaml
+# Cloud-init is S1 Infrastructure Substrate scope (ADR-003).