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

versioncontrol/compose.yml

@@ -6,7 +6,7 @@ services:
     environment:
       - USER_UID=1000
       - USER_GID=1000
-      - GITEA__server__ROOT_URL=https://code.lazyworkhorse.net
+      - GITEA__server__ROOT_URL=https://code.${DOMAIN}
       - GITEA__actions__ENABLED=true
       - SSH_PORT=2222
       - SSH_LISTEN_PORT=2222
@@ -23,21 +23,21 @@ services:
       - "traefik.enable=true"
 
       # HTTP -> HTTPS Redirect
-      - "traefik.http.routers.gitea-http.rule=Host(`code.lazyworkhorse.net`)"
+      - "traefik.http.routers.gitea-http.rule=Host(`code.${DOMAIN}`)"
       - "traefik.http.routers.gitea-http.entrypoints=web"
       - "traefik.http.routers.gitea-http.middlewares=redirect-to-https"
       - "traefik.http.middlewares.redirect-to-https.redirectscheme.scheme=https"
 
       # HTTPS Router
-      - "traefik.http.routers.gitea-https.rule=Host(`code.lazyworkhorse.net`)"
+      - "traefik.http.routers.gitea-https.rule=Host(`code.${DOMAIN}`)"
       - "traefik.http.routers.gitea-https.entrypoints=websecure"
       - "traefik.http.routers.gitea-https.tls=true"
       - "traefik.http.routers.gitea-https.tls.certresolver=njalla"
       - "traefik.http.routers.gitea-https.middlewares=gitea-home-redirect"
 
       # The Redirect Logic - Using single quotes to allow backslashes
-      - 'traefik.http.middlewares.gitea-home-redirect.redirectregex.regex=^https://code\.lazyworkhorse\.net/?$$'
-      - 'traefik.http.middlewares.gitea-home-redirect.redirectregex.replacement=https://code.lazyworkhorse.net/gortium'
+      - 'traefik.http.middlewares.gitea-home-redirect.redirectregex.regex=^https://code\.${DOMAIN}/?$$'
+      - 'traefik.http.middlewares.gitea-home-redirect.redirectregex.replacement=https://code.${DOMAIN}/gortium'
       - "traefik.http.middlewares.gitea-home-redirect.redirectregex.permanent=true"
 
       # Internal Routing
@@ -47,7 +47,7 @@ services:
     image: gitea/act_runner:latest
     container_name: act_runner
     environment:
-      - GITEA_INSTANCE_URL=https://code.lazyworkhorse.net
+      - GITEA_INSTANCE_URL=https://code.${DOMAIN}
       - GITEA_RUNNER_REGISTRATION_TOKEN=${GITEA_RUNNER_TOKEN}
       - GITEA_RUNNER_NAME=ai-host-runner
       - GITEA_RUNNER_LABELS=ubuntu-latest:docker://catthehacker/ubuntu:full-22.04,nixos-builder:docker://nixos/nix