feat: add Promtail, Loki, and Grafana log aggregation stack (refs #86)

- Add Promtail for Docker log scraping with container discovery
- Add Loki for log storage with 30-day retention
- Add Grafana with Loki datasource auto-provisioned
- Add IP whitelist middleware restricting Grafana to RFC1918 ranges
- Container count: 6 → 9

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

config/loki/config.yml

@@ -0,0 +1,32 @@
+auth_enabled: false
+
+server:
+  http_listen_port: 3100
+
+ingester:
+  lifecycler:
+    ring:
+      kvstore:
+        store: inmemory
+      replication_factor: 1
+
+schema_config:
+  configs:
+    - from: 2020-01-01
+      store: boltdb-shipper
+      object_store: filesystem
+      schema: v11
+      index:
+        prefix: index_
+        period: 24h
+
+storage_config:
+  boltdb_shipper:
+    active_index_directory: /loki/boltdb-shipper-active
+    cache_location: /loki/boltdb-shipper-cache
+    shared_store: filesystem
+  filesystem:
+    directory: /loki/chunks
+
+limits_config:
+  retention_period: 720h  # 30 days