refactor: replace CADDY_MANAGER with DEPLOY_ENV for instance-role awareness

DEPLOY_ENV=production now marks the primary instance globally - used for
Caddy ownership, the Dev/Prod header badge, and Caddy UI gating. Removes
build-time VITE_DEPLOY_ENV/import.meta.env.DEV from the header in favour
of the runtime API response (isProduction field in /api/auth/config).

deploy/proxmox-ghostgrid.sh

@@ -190,8 +190,8 @@ msg_info "Creating .env file for each instance"
 for d in "${APP_DIR}" "${DEV_DIR}"; do
   SECRET="$(openssl rand -hex 32)"
   run "printf 'JWT_SECRET=\"%s\"\n' '${SECRET}' > ${d}/.env && chown ghostgrid:ghostgrid ${d}/.env && chmod 600 ${d}/.env"
-  # Only the production instance owns the shared Caddy (one Caddy per container).
-  [[ "$d" == "${APP_DIR}" ]] && run "printf 'CADDY_MANAGER=true\n' >> ${d}/.env"
+  # Only the production instance owns Caddy and shows "Production" in the UI.
+  [[ "$d" == "${APP_DIR}" ]] && run "printf 'DEPLOY_ENV=production\n' >> ${d}/.env"
 done
 msg_ok ".env files created (main + dev)"