Docs: autogenerate inventory & buildClan model

docs/nix/flake-module.nix

@@ -8,6 +8,7 @@
       ...
     }:
     let
+      buildClanOptions = self'.legacyPackages.clan-internals-docs;
       # Simply evaluated options (JSON)
       # { clanCore = «derivation JSON»; clanModules = { ${name} = «derivation JSON» }; }
       jsonDocs = import ./get-module-docs.nix {
@@ -67,6 +68,9 @@
             # A file that contains the links to all clanModule docs
             export CLAN_MODULES=${clanModulesFileInfo}
 
+            # buildClan options
+            export BUILD_CLAN_PATH=${buildClanOptions}/share/doc/nixos/options.json
+
             mkdir $out
 
             # The python script will place mkDocs files in the output directory