feat(packages): add nftablesbuilder package

Web interface to manage nftables rules with drag-and-drop rule creation.

Upstream source is incomplete (missing settings crate, no GUI build
tooling), so the package builds the Rust workspace from the pinned
commit with a patched-in settings crate (schema recovered from official
release artifacts) and reuses the prebuilt GUI from the hash-pinned
release tarball on nftablesbuilder.eu.

packages/nftablesbuilder/settings.example

@@ -0,0 +1,17 @@
+[connection]
+port = 1969
+
+[paths]
+savepath = "/var/lib/nftablesbuilder"
+htmlpath = "/run/current-system/sw/share/nftablesbuilder/html"
+
+[files]
+nft = "/run/current-system/sw/bin/nft"
+test = "/tmp/nftables.conf"
+conf = "/etc/nftables.conf"
+webserver = "/run/current-system/sw/libexec/nftablesbuilder/webserver"
+tlskey = "/var/lib/nftablesbuilder/nftables.key"
+tlscert = "/var/lib/nftablesbuilder/nftables.crt"
+
+[commands]
+reload = "systemctl reload nftables"