monitoring02: add Loki service

Add standalone Loki service module (services/loki/) with same config as
monitoring01 and import it on monitoring02. Update Grafana Loki datasource
to localhost. Defer Tempo and Pyroscope migration (not actively used).

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

services/loki/default.nix

@@ -0,0 +1,58 @@
+{ ... }:
+{
+  services.loki = {
+    enable = true;
+    configuration = {
+      auth_enabled = false;
+
+      server = {
+        http_listen_port = 3100;
+      };
+      common = {
+        ring = {
+          instance_addr = "127.0.0.1";
+          kvstore = {
+            store = "inmemory";
+          };
+        };
+        replication_factor = 1;
+        path_prefix = "/var/lib/loki";
+      };
+      schema_config = {
+        configs = [
+          {
+            from = "2024-01-01";
+            store = "tsdb";
+            object_store = "filesystem";
+            schema = "v13";
+            index = {
+              prefix = "loki_index_";
+              period = "24h";
+            };
+          }
+        ];
+      };
+      storage_config = {
+        filesystem = {
+          directory = "/var/lib/loki/chunks";
+        };
+      };
+      compactor = {
+        working_directory = "/var/lib/loki/compactor";
+        compaction_interval = "10m";
+        retention_enabled = true;
+        retention_delete_delay = "2h";
+        retention_delete_worker_count = 150;
+        delete_request_store = "filesystem";
+      };
+      limits_config = {
+        retention_period = "30d";
+        ingestion_rate_mb = 10;
+        ingestion_burst_size_mb = 20;
+        max_streams_per_user = 10000;
+        max_query_series = 500;
+        max_query_parallelism = 8;
+      };
+    };
+  };
+}