loki: add basic auth for log push and dual-ship promtail

- Loki bound to localhost, Caddy reverse proxy with basic_auth
- Vault secret (shared/loki/push-auth) for password, bcrypt hash
  generated at boot for Caddy environment
- Promtail dual-ships to monitoring01 (direct) and loki.home.2rjus.net
  (with basic auth), conditional on vault.enable
- Terraform: new shared loki-push policy added to all AppRoles

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

terraform/vault/approle.tf

@@ -26,6 +26,17 @@ path "secret/data/shared/nixos-exporter/*" {
 EOT
 }
 
+# Shared policy for Loki push authentication (all hosts push logs)
+resource "vault_policy" "loki_push" {
+  name = "loki-push"
+
+  policy = <<EOT
+path "secret/data/shared/loki/*" {
+  capabilities = ["read", "list"]
+}
+EOT
+}
+
 # Define host access policies
 locals {
   host_policies = {
@@ -138,7 +149,7 @@ resource "vault_approle_auth_backend_role" "hosts" {
   backend   = vault_auth_backend.approle.path
   role_name = each.key
   token_policies = concat(
-    ["${each.key}-policy", "homelab-deploy", "nixos-exporter"],
+    ["${each.key}-policy", "homelab-deploy", "nixos-exporter", "loki-push"],
     lookup(each.value, "extra_policies", [])
   )