Switch the Go build invocation to target the cmd/gluetun package directory (./cmd/gluetun/) in both ct/gluetun.sh and install/gluetun-install.sh, and ensure modules are downloaded during install (go mod download). In the installer, create /opt/gluetun-data and add a symlink /gluetun -> /opt/gluetun-data, update STORAGE/PUBLICIP/PORT file paths to use /gluetun, add PPROF_ENABLED=no to the default .env, and add UnsetEnvironment=USER to the systemd unit to avoid inheriting the USER environment. These changes standardize build behavior and relocate runtime data to a consistent /gluetun path.
