Add HA for CV and Docs: zero-downtime deploys (#273)

## Summary
- Set `replicas: 2` with `maxUnavailable: 0` / `maxSurge: 1` on CV and Docs deployments so rolling updates never drop below 2 ready pods
- Add PodDisruptionBudgets (`minAvailable: 1`) to protect against node drains and cluster maintenance
- Add Fly.io cache purge step to `cv-deploy.yaml` workflow (docs already had this) so CV deploys don't serve stale cached content

## Deployment and Testing
- [ ] `argocd app diff cv` / `argocd app diff docs` from branch
- [ ] Deploy from branch: `argocd app set cv --revision feature/ha-cv-docs-zero-downtime && argocd app sync cv`
- [ ] Verify 2 pods running: `kubectl get pods -n cv --context=minikube-indri`
- [ ] Test rolling restart: `kubectl rollout restart deployment/cv -n cv --context=minikube-indri`
- [ ] During rollout, confirm continuous availability via `curl -I https://cv.eblu.me`
- [ ] After merge: reset ArgoCD to main, re-sync both apps

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/273

docs/changelog.d/feature/ha-cv-docs-zero-downtime.infra.md

@@ -0,0 +1 @@
+Add HA (2 replicas + PDB) for CV and Docs services for zero-downtime deploys.