feat(observability): persist standalone stack data and expose ports via env

- Switch docker-compose.observability.yml from named volumes to host
  bind mounts under OBSERVABILITY_DATA_ROOT, defaulting to
  ./observability-data.
- Make all service ports configurable via environment variables
  (PROMETHEUS_PORT, LOKI_PORT, ALLOY_PORT, GRAFANA_PORT,
  ALERTMANAGER_PORT, NODE_EXPORTER_PORT).
- Add VITE_GRAFANA_URL handling to ObservabilityPage so Grafana links
  point to the configured standalone instance.
- Update docs/observability-runbooks.md with the env variable table,
  reachable-web-UI table, and backup/restore instructions for the new
  host-directory layout.

docker-compose.observability.yml

@@ -4,6 +4,8 @@
 # Alloy and Node Exporter without the rest of Manage. It exposes the usual
 # ports directly; no Traefik or OIDC integration is required.
 #
+#   cp .env.example .env
+#   # optionally edit OBSERVABILITY_* paths and ports
 #   docker compose -f docker-compose.observability.yml up -d
 #
 # Then open Grafana at http://localhost:3000 (admin / admin by default).
@@ -27,9 +29,9 @@ services:
       - ./monitoring/prometheus/prometheus.standalone.yml:/etc/prometheus/prometheus.yml:ro
       - ./monitoring/prometheus/rules:/etc/prometheus/rules:ro
       - ./monitoring/prometheus/file-sd:/etc/prometheus/file-sd:ro
-      - prometheus_data:/prometheus
+      - ${OBSERVABILITY_DATA_ROOT:-./observability-data}/prometheus:/prometheus
     ports:
-      - "9090:9090"
+      - "${PROMETHEUS_PORT:-9090}:9090"
     networks:
       - monitoring
     restart: unless-stopped
@@ -54,9 +56,9 @@ services:
     command: -config.file=/etc/loki/loki.yml
     volumes:
       - ./monitoring/loki/loki.yml:/etc/loki/loki.yml:ro
-      - loki_data:/loki
+      - ${OBSERVABILITY_DATA_ROOT:-./observability-data}/loki:/loki
     ports:
-      - "3100:3100"
+      - "${LOKI_PORT:-3100}:3100"
     networks:
       - monitoring
     restart: unless-stopped
@@ -86,6 +88,9 @@ services:
       - ./monitoring/alloy/config.alloy:/etc/alloy/config.alloy:ro
       - /var/run/docker.sock:/var/run/docker.sock:ro
       - /var/lib/docker/containers:/var/lib/docker/containers:ro
+      - ${OBSERVABILITY_DATA_ROOT:-./observability-data}/alloy:/var/lib/alloy
+    ports:
+      - "${ALLOY_PORT:-12345}:12345"
     networks:
       - monitoring
     depends_on:
@@ -123,9 +128,9 @@ services:
     volumes:
       - ./monitoring/grafana/grafana.ini:/etc/grafana/grafana.ini:ro
       - ./monitoring/grafana/provisioning:/etc/grafana/provisioning:ro
-      - grafana_data:/var/lib/grafana
+      - ${OBSERVABILITY_DATA_ROOT:-./observability-data}/grafana:/var/lib/grafana
     ports:
-      - "3000:3000"
+      - "${GRAFANA_PORT:-3000}:3000"
     networks:
       - monitoring
     depends_on:
@@ -164,9 +169,9 @@ services:
       ALERT_EMAIL_TO: ${ALERT_EMAIL_TO:-admin@example.com}
     volumes:
       - ./monitoring/alertmanager/alertmanager.yml:/etc/alertmanager/alertmanager.yml:ro
-      - alertmanager_data:/alertmanager
+      - ${OBSERVABILITY_DATA_ROOT:-./observability-data}/alertmanager:/alertmanager
     ports:
-      - "9093:9093"
+      - "${ALERTMANAGER_PORT:-9093}:9093"
     networks:
       - monitoring
     restart: unless-stopped
@@ -193,7 +198,7 @@ services:
     volumes:
       - /:/host:ro,rslave
     ports:
-      - "9100:9100"
+      - "${NODE_EXPORTER_PORT:-9100}:9100"
     networks:
       - monitoring
     restart: unless-stopped
@@ -214,9 +219,3 @@ services:
 
 networks:
   monitoring:
-
-volumes:
-  prometheus_data:
-  loki_data:
-  grafana_data:
-  alertmanager_data: