secrets: migrate all hosts from sops to OpenBao vault

Replace sops-nix secrets with OpenBao vault secrets across all hosts.
Hardcode root password hash, add extractKey option to vault-secrets
module, update Terraform with secrets/policies for all hosts, and
create AppRole provisioning playbook.

Hosts migrated: ha1, monitoring01, ns1, ns2, http-proxy, nix-cache01
Wave 1 hosts (nats1, jelly01, pgdb1) get AppRole policies only.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/plans/sops-to-openbao-migration.md

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+# Sops to OpenBao Secrets Migration Plan
+
+## Status: In Progress
+
+## Overview
+
+Migrate all hosts from sops-nix secrets to OpenBao (vault) secrets management. Pilot with ha1, then roll out to remaining hosts in waves.
+
+## Pre-requisites (completed)
+
+1. Hardcoded root password hash in `system/root-user.nix` (removes sops dependency for all hosts)
+2. Added `extractKey` option to `system/vault-secrets.nix` (extracts single key as file)
+
+## Deployment Order
+
+### Pilot: ha1
+- Terraform: shared/backup/password secret, ha1 AppRole policy
+- Provision AppRole credentials via `playbooks/provision-approle.yml`
+- NixOS: vault.enable + backup-helper vault secret
+
+### Wave 1: nats1, jelly01, pgdb1
+- No service secrets (only root password, already handled)
+- Just need AppRole policies + credential provisioning
+
+### Wave 2: monitoring01
+- 3 secrets: backup password, nats nkey, pve-exporter config
+- Updates: alerttonotify.nix, pve.nix, configuration.nix
+
+### Wave 3: ns1, then ns2 (critical - deploy ns1 first, verify, then ns2)
+- DNS zone transfer key (shared/dns/xfer-key)
+
+### Wave 4: http-proxy
+- WireGuard private key
+
+### Wave 5: nix-cache01
+- Cache signing key + Gitea Actions token
+
+### Wave 6: ca (DEFERRED - waiting for PKI migration)
+
+### Skipped: auth01 (decommissioned)
+
+## Terraform variables needed
+
+User must extract from sops and add to `terraform/vault/terraform.tfvars`:
+
+| Variable | Source |
+|----------|--------|
+| `backup_helper_secret` | `sops -d secrets/secrets.yaml` |
+| `ns_xfer_key` | `sops -d secrets/secrets.yaml` |
+| `nats_nkey` | `sops -d secrets/secrets.yaml` |
+| `pve_exporter_config` | `sops -d secrets/monitoring01/pve-exporter.yaml` |
+| `wireguard_private_key` | `sops -d secrets/http-proxy/wireguard.yaml` |
+| `cache_signing_key` | `sops -d secrets/nix-cache01/cache-secret` |
+| `actions_token_1` | `sops -d secrets/nix-cache01/actions_token_1` |
+
+## Provisioning AppRole credentials
+
+```bash
+export BAO_ADDR='https://vault01.home.2rjus.net:8200'
+export BAO_TOKEN='<root-token>'
+nix develop -c ansible-playbook playbooks/provision-approle.yml -e hostname=<host>
+```
+
+## Verification (per host)
+
+1. `systemctl status vault-secret-*` - all secret fetch services succeeded
+2. Check secret files exist at expected paths with correct permissions
+3. Verify dependent services are running
+4. Check `/var/lib/vault/cache/` is populated (fallback ready)
+5. Reboot host to verify boot-time secret fetching works