bingo: add a reachability monitor for the status page

datacenterbingo gets a public page showing whether each datacenter's
network answers. The probing lives here, next to the schema and the
admin, since the public site only has a read-only role.

bin/monitor runs as a second container from the same image. Once a
minute it opens one TCP connection to every active target (a handshake
or a refusal both count as answered) and folds the results into
5-minute rows per datacenter, plus a per-bucket row for control hosts in
Russia, so a lost vantage point isn't mistaken for dark sites. Rows are
kept 30 days. Targets are managed at /admin/bingo/monitor; only hosts a
public source ties to that one site belong there.

Migration 017 also grants the new tables to the bingo role, so the
public site can read them without a storage redeploy.

Assisted-by: Claude:opus-5-5

docker-compose.yml

@@ -19,6 +19,25 @@ services:
       - "traefik.http.routers.asxpio.service=asxpio"
       - "traefik.http.services.asxpio.loadbalancer.server.port=3000"
 
+  # Reachability worker for datacenterbingo's status page (bin/monitor).
+  # Same image; the deploy's sed sets both image lines.
+  asxpio-monitor:
+    image: asxpio:latest
+    container_name: asxpio-monitor
+    restart: unless-stopped
+    env_file: .env
+    command: ["ruby", "bin/monitor"]
+    networks:
+      - storage # postgres; not internal, so probes reach the internet
+    mem_limit: 256m
+    healthcheck:
+      # The worker touches its heartbeat after every round (60 s).
+      test: ["CMD", "ruby", "-e", "exit(Time.now - File.mtime('/tmp/monitor.heartbeat') < 300 ? 0 : 1)"]
+      interval: 60s
+      timeout: 10s
+      start_period: 120s
+      retries: 3
+
 networks:
   traefik:
     external: true