feat(monitoring): integrate Promtail for centralized log collection via Loki

Loki was already running but had no log shipper. Adds Promtail to collect
Docker logs from all 66 containers with automatic tier labeling (infra,
auth, core, app, matrix, games) and a Grafana Logs Explorer dashboard.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.macmini.yml

@@ -1635,6 +1635,25 @@ services:
       retries: 3
       start_period: 15s
 
+  promtail:
+    image: grafana/promtail:3.0.0
+    container_name: mana-mon-promtail
+    restart: always
+    mem_limit: 96m
+    command: -config.file=/etc/promtail/config.yaml -config.expand-env=true
+    volumes:
+      - ./docker/promtail:/etc/promtail:ro
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+    depends_on:
+      loki:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "wget", "--no-verbose", "--tries=1", "--spider", "http://127.0.0.1:9080/ready"]
+      interval: 300s
+      timeout: 10s
+      retries: 3
+      start_period: 10s
+
   pushgateway:
     image: prom/pushgateway:v1.7.0
     container_name: mana-mon-pushgateway