chore(buildClan): make buildClan and flake-parts return identical outputs

lib/build-clan/public.nix

@@ -0,0 +1,17 @@
+/**
+  Publicly exported attribute names
+  These are mapped from 'options.clan.{name}' into 'flake.{name}'
+  For example "clanInternals" will be exposed as "flake.clan.clanInternals"
+  This list is used to guarantee equivalent attribute sets for both flake-parts and buildClan users.
+*/
+{
+  # flake.clan.{name} <- clanInternals.{name}
+  clan = [
+    "templates"
+  ];
+  # flake.{name} <- clan.{name}
+  topLevel = [
+    "clanInternals"
+    "nixosConfigurations"
+  ];
+}