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>

services/monitoring/alerttonotify.nix

@@ -1,12 +1,18 @@
 { pkgs, config, ... }:
 {
-  sops.secrets."nats_nkey" = { };
+  vault.secrets.nats-nkey = {
+    secretPath = "shared/nats/nkey";
+    extractKey = "nkey";
+    outputDir = "/run/secrets/nats_nkey";
+    services = [ "alerttonotify" ];
+  };
+
   systemd.services."alerttonotify" = {
     enable = true;
     wants = [ "network-online.target" ];
     after = [
       "network-online.target"
-      "sops-nix.service"
+      "vault-secret-nats-nkey.service"
     ];
     wantedBy = [ "multi-user.target" ];
     restartIfChanged = true;

services/monitoring/pve.nix

@@ -1,14 +1,16 @@
 { config, ... }:
 {
-  sops.secrets.pve_exporter = {
-    format = "yaml";
-    sopsFile = ../../secrets/monitoring01/pve-exporter.yaml;
-    key = "";
+  vault.secrets.pve-exporter = {
+    secretPath = "hosts/monitoring01/pve-exporter";
+    extractKey = "config";
+    outputDir = "/run/secrets/pve_exporter";
     mode = "0444";
+    services = [ "prometheus-pve-exporter" ];
   };
+
   services.prometheus.exporters.pve = {
     enable = true;
-    configFile = config.sops.secrets.pve_exporter.path;
+    configFile = "/run/secrets/pve_exporter";
     collectors = {
       cluster = false;
       replication = false;