docs(vibe): add erp/ guidebook (Dolibarr deployment + backup/recovery + ops)

Dedicated tree-docs guidebook under vibe/guidebooks/erp/ for the lab's most
data-critical app, cross-linked from the applications hub (bidirectional):

- README.md             : Dolibarr 22.0.4 on Postgres; data-criticality; overview
  diagram; the Vault-unseal-before-scale recovery ordering (CAUTION).
- deployment.md         : upstream image + custom entrypoint (MySQL->psql), the
  50Gi Longhorn RWX documents PVC, Vault CRDs + the shared app_roles iac, init
  scripts (conf.php creds, table-ownership), ingress, CI.
- backup-and-recovery.md: the Ansible CronJob pg_dump (daily 04:00, 15-day
  retention) + restore Job (scale-0 -> restore -> scale-1); the cluster recovery
  ordering (Longhorn -> Vault unseal -> erp scale-up).
- operations.md         : the read-only bin/arcodange CLI, static/company.json,
  Deno+Playwright tests, day-2 ops.

erp code via full gitea URLs; CLUSTER_RECOVERY.md by name; 2 mermaid diagrams
MCP-validated; zero dead links.

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

vibe/guidebooks/README.md

@@ -39,6 +39,7 @@ flowchart LR
 | [Tools](tools/README.md) | Deep dive into the lab platform services in the `tools` namespace (Vault+VSO, Prometheus, Grafana, CrowdSec, poolers, Redis, Plausible, ClickHouse) | ✅ Active |
 | [CMS](cms/README.md) | Deep dive into the public Nuxt site arcodange.fr + its Cloudflare DNS/tunnel/Turnstile and Zoho email IaC | ✅ Active |
 | [Applications](applications/README.md) | The deployed apps and the common pattern they share — webapp (Go + Postgres) and url-shortener (Rust + SQLite); erp has its own guidebook | ✅ Active |
+| [ERP](erp/README.md) | The lab’s Dolibarr ERP — its deployment on Postgres, its document storage + backup/restore, and the read-only ops CLI (the most data-critical app) | ✅ Active |
 
 ## Rules to contribute