Stability checkpoint — OVH timing docs

Single doc commit since stable-v1.0.39 (b450bac) :

📚 Documentation
- docs(ovh): document real per-resource apply/destroy timings —
  measured 2026-04-23 on first real apply (Q2 activation). Per-
  resource breakdown : network 48s + subnet 4s + kube 4m55s +
  nodepool 6m45s = ~12 min total. Destroy ~2m08s. ~40% faster
  than GKE Autopilot equivalent.
- README documents the 2 first-apply gotchas already fixed in
  ada4896 (private_network_id UUID + b2-7 lowercase flavor).

Post-merge main pipeline #767 green on SHA 8017022.