refactor: use $DOMAIN env var instead of hardcoded lazyworkhorse.net

Replace all hardcoded lazyworkhorse.net references in compose files
with ${DOMAIN} variable substitution. Create .env.production and
.env.staging environment files. Update Makefile with ENV selection
(--env-file support) and staging/production targets.

Changes:
- All 13 compose YAML files: lazyworkhorse.net -> ${DOMAIN}
- New .env.production (DOMAIN=lazyworkhorse.net)
- New .env.staging (DOMAIN=staging.lazyworkhorse.net)
- Makefile: ENV var, --env-file flag, staging/production targets
- Gitea redirect regex updated for variable substitution
- CI workflow checkout URLs left hardcoded (infrastructure refs)
- Dockerfile SSH host refs left hardcoded (infrastructure refs)

Deploy: make ENV=staging all_up  or  make staging
        make ENV=production all_up  or  make production

coms/compose.yml

@@ -25,10 +25,10 @@ services:
         condition: service_healthy
     labels:
       - "traefik.enable=true"
-      - "traefik.http.routers.matrix-http.rule=Host(`matrix.lazyworkhorse.net`)"
+      - "traefik.http.routers.matrix-http.rule=Host(`matrix.${DOMAIN}`)"
       - "traefik.http.routers.matrix-http.entrypoints=web"
       - "traefik.http.routers.matrix-http.middlewares=redirect-to-https"
-      - "traefik.http.routers.matrix-https.rule=Host(`matrix.lazyworkhorse.net`)"
+      - "traefik.http.routers.matrix-https.rule=Host(`matrix.${DOMAIN}`)"
       - "traefik.http.routers.matrix-https.entrypoints=websecure"
       - "traefik.http.routers.matrix-https.tls=true"
       - "traefik.http.routers.matrix-https.tls.certresolver=njalla"
@@ -62,10 +62,10 @@ services:
       - coms_net
     labels:
       - "traefik.enable=true"
-      - "traefik.http.routers.synapse-admin-http.rule=Host(`synadm.lazyworkhorse.net`)"
+      - "traefik.http.routers.synapse-admin-http.rule=Host(`synadm.${DOMAIN}`)"
       - "traefik.http.routers.synapse-admin-http.entrypoints=web"
       - "traefik.http.routers.synapse-admin-http.middlewares=redirect-to-https"
-      - "traefik.http.routers.synapse-admin-https.rule=Host(`synadm.lazyworkhorse.net`)"
+      - "traefik.http.routers.synapse-admin-https.rule=Host(`synadm.${DOMAIN}`)"
       - "traefik.http.routers.synapse-admin-https.entrypoints=websecure"
       - "traefik.http.routers.synapse-admin-https.tls=true"
       - "traefik.http.routers.synapse-admin-https.tls.certresolver=njalla"
@@ -88,12 +88,12 @@ services:
   #     - "traefik.enable=true"
   #
   #     # HTTP → HTTPS
-  #     - "traefik.http.routers.rns-http.rule=Host(`nomad.lazyworkhorse.net`)"
+  #     - "traefik.http.routers.rns-http.rule=Host(`nomad.${DOMAIN}`)"
   #     - "traefik.http.routers.rns-http.entrypoints=web"
   #     - "traefik.http.routers.rns-http.middlewares=redirect-to-https"
   #
   #     # HTTPS protected by Authelia
-  #     - "traefik.http.routers.rns-https.rule=Host(`nomad.lazyworkhorse.net`)"
+  #     - "traefik.http.routers.rns-https.rule=Host(`nomad.${DOMAIN}`)"
   #     - "traefik.http.routers.rns-https.entrypoints=websecure"
   #     - "traefik.http.routers.rns-https.tls=true"
   #     - "traefik.http.routers.rns-https.tls.certresolver=njalla"