fix: resolve staging deployment issues with Traefik, Loki, and Alloy (refs #105)

- Exclude blue-green.yml from staging Traefik by mounting dynamic-staging/
  directory (only grafana.yml + middleware.yml) instead of dynamic/ which
  contains production-only blue-green routing config
- Disable Loki healthcheck: distroless image has no /bin/sh so CMD-SHELL
  healthchecks cannot execute; Alloy and Grafana verify Loki connectivity
- Fix Alloy healthcheck: replace wget (not in image) with bash /dev/tcp
- Add Grafana staging domain override (logs.staging.motovaultpro.com)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -276,10 +276,9 @@ services:
     networks:
       - backend
     healthcheck:
-      test: ["CMD-SHELL", "wget -q --spider http://localhost:3100/ready || exit 1"]
-      interval: 30s
-      timeout: 10s
-      retries: 3
+      # Loki 3.x uses a distroless image with no shell or HTTP client.
+      # Disable in-container healthcheck; Alloy and Grafana verify connectivity.
+      disable: true
     logging:
       driver: json-file
       options:
@@ -305,7 +304,7 @@ services:
     depends_on:
       - mvp-loki
     healthcheck:
-      test: ["CMD-SHELL", "wget -q --spider http://localhost:12345/ready || exit 1"]
+      test: ["CMD-SHELL", "bash -c 'echo > /dev/tcp/localhost/12345'"]
       interval: 30s
       timeout: 10s
       retries: 3