terraform: add nixos-exporter shared policy

- Create shared policy granting all hosts access to nixos-exporter nkey
- Add policy to both manual and generated host AppRoles
- Remove duplicate kanidm01/monitoring02 entries from hosts-generated.tf

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

terraform/vault/hosts-generated.tf

@@ -33,18 +33,6 @@ locals {
         "secret/data/shared/homelab-deploy/*",
       ]
     }
-    "kanidm01" = {
-      paths = [
-        "secret/data/hosts/kanidm01/*",
-        "secret/data/kanidm/*",
-      ]
-    }
-    "monitoring02" = {
-      paths = [
-        "secret/data/hosts/monitoring02/*",
-      ]
-    }
-  
   }
 
   # Placeholder secrets - user should add actual secrets manually or via tofu
@@ -74,7 +62,7 @@ resource "vault_approle_auth_backend_role" "generated_hosts" {
 
   backend            = vault_auth_backend.approle.path
   role_name          = each.key
-  token_policies     = ["host-${each.key}", "homelab-deploy"]
+  token_policies     = ["host-${each.key}", "homelab-deploy", "nixos-exporter"]
   secret_id_ttl      = 0 # Never expire (wrapped tokens provide time limit)
   token_ttl          = 3600
   token_max_ttl      = 3600