Rework the nftables module so Webmin manages its saved nftables configuration as the source of truth instead of directly editing the live ruleset. Add an active ruleset view for inspecting live tables and importing copies into Webmin-managed config if needed, track managed and imported tables with metadata, and prevent externally managed tables from being overwritten during apply.
Co-authored-by: Copilot <copilot@github.com>
