also refactor nixos modules

modules/nixos/services/observability/loki.nix

@@ -0,0 +1,52 @@
+{
+  pkgs,
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib.modules) mkIf;
+  inherit (lib.options) mkEnableOption;
+
+  cfg = config.sneeuwvlok.services.observability.loki;
+in {
+  options.sneeuwvlok.services.observability.loki = {
+    enable = mkEnableOption "enable Grafana Loki";
+  };
+
+  config = mkIf cfg.enable {
+    services.loki = {
+      enable = true;
+      configuration = {
+        auth_enabled = false;
+
+        server = {
+          http_listen_port = 9003;
+        };
+
+        common = {
+          ring = {
+            instance_addr = "127.0.0.1";
+            kvstore.store = "inmemory";
+          };
+          replication_factor = 1;
+          path_prefix = "/tmp/loki";
+        };
+
+        schema_config.configs = [
+          {
+            from = "2025-01-01";
+            store = "tsdb";
+            object_store = "filesystem";
+            schema = "v13";
+            index = {
+              prefix = "index_";
+              period = "24h";
+            };
+          }
+        ];
+      };
+    };
+
+    networking.firewall.allowedTCPPorts = [9003];
+  };
+}