feat(deploy): prod compose split + host-memory monitoring (Stage 18)

Split the contour across the two prod hosts and retune for the small main host:

- Gate vpn+bot to the telegram-local profile. The CI test deploy now passes
  --profile telegram-local so the test contour still brings them; the prod main
  host omits both, and the prod bot runs standalone from docker-compose.bot.yml.
- docker-compose.prod.yml (main-host overlay): publish caddy 80/443 (no host
  caddy in prod; caddy owns ACME) and gateway 9443 (the remote bot dials in over
  mTLS); GOMAXPROCS=2, smaller memory caps and 7d Prometheus retention for the
  2 vCPU / 1.9 GiB host. It launches deliberately undersized; resize reactively.
- docker-compose.bot.yml: standalone bot for the tg host (no VPN, OTLP off since
  otelcol is unreachable from there, dials the main host's bot-link).
- Add node_exporter + a Prometheus scrape so host memory pressure (the OOM
  signal on the tight main host), not just per-container docker_stats, is visible.
- Soften AWG_CONF to a default: only the profiled vpn sidecar consumes it, and
  compose interpolates profiled-out services too, so prod must not require it.

deploy/docker-compose.prod.yml

@@ -0,0 +1,92 @@
+# Production main-host overlay, applied on top of docker-compose.yml on the main host:
+#   docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d
+#
+# It (1) publishes caddy 80/443 — there is no host caddy in prod, so the contour caddy
+# owns the edge and does its own ACME on CADDY_SITE_ADDRESS — and the gateway bot-link
+# :9443 the remote bot dials in over mTLS; and (2) retunes the R7 limits down for the
+# 2 vCPU / 1.9 GiB host (GOMAXPROCS=2, smaller memory caps, shorter Prometheus
+# retention). The contour launches deliberately undersized at zero players; the added
+# node_exporter + Grafana watch host memory so it can be resized at Selectel when
+# traffic arrives.
+#
+# The bot + its VPN sidecar are absent here (the telegram-local profile is not
+# activated); the prod bot runs on its own host from docker-compose.bot.yml.
+
+services:
+  caddy:
+    ports:
+      - "80:80"
+      - "443:443"
+    deploy:
+      resources:
+        limits:
+          memory: 96M
+
+  gateway:
+    ports:
+      - "9443:9443"
+    environment:
+      # 2 vCPU host: align the Go scheduler with the cgroup quota (R7's 3 needs 3 cores).
+      GOMAXPROCS: "2"
+    deploy:
+      resources:
+        limits:
+          cpus: "2.0"
+          memory: 384M
+
+  backend:
+    deploy:
+      resources:
+        limits:
+          memory: 384M
+
+  postgres:
+    deploy:
+      resources:
+        limits:
+          memory: 384M
+
+  validator:
+    deploy:
+      resources:
+        limits:
+          memory: 96M
+
+  landing:
+    deploy:
+      resources:
+        limits:
+          memory: 64M
+
+  otelcol:
+    deploy:
+      resources:
+        limits:
+          memory: 256M
+
+  prometheus:
+    command:
+      - --config.file=/etc/prometheus/prometheus.yml
+      - --storage.tsdb.retention.time=7d
+    deploy:
+      resources:
+        limits:
+          memory: 256M
+
+  tempo:
+    deploy:
+      resources:
+        limits:
+          memory: 384M
+
+  grafana:
+    deploy:
+      resources:
+        limits:
+          memory: 256M
+
+  postgres_exporter:
+    deploy:
+      resources:
+        limits:
+          memory: 64M