feat(safety-net): create WP-0004, update preflight for OAS 5-repo layout

- workplans/RAIL-BS-WP-0004-safety-net.md: ADR-001 workplan file for
  current-env-safety-net workstream (7e8b0c20), T01-T04 done, T05-T06 todo
- tools/cmd/railiance-preflight: update REPOS to OAS S1-S5 stack
  (railiance-infra/cluster/platform/enablement/apps) + project repos;
  remove stale railiance-bootstrap reference
- docs/backup-restore.md: fix Step 5 clone commands to current repo names
- Makefile: add make backup and make preflight targets

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

Makefile

@@ -2,6 +2,14 @@
 
 INVENTORY ?= ansible/hosts.ini
 
+##@ Safety Net
+
+backup: ## Backup postgres + config to Nextcloud (age-encrypted)
+	bin/railiance backup
+
+preflight: ## Pre-migration safety gate — must pass before cluster work
+	bin/railiance preflight
+
 ##@ Kubernetes
 
 k3s-install: ## Install k3s and Helm on all inventory hosts