Expand the systemd installer so it can perform a complete native
installation with sensible defaults: copy the checkout into the target
app directory, create runtime directories, write the environment file,
install dependencies, configure systemd units, and optionally configure
nginx.
Add a staff-only Django self-check page that verifies runtime settings,
required binaries, writable paths, database connectivity, global config
state, and systemd service status when available.
Document installer overrides and expose the self-check from the main
navigation.
