clan: Add autoloaded clanModules from flake inputs. Rename 'directory' to 'self' in buildClan

lib/build-clan/auto-imports.nix

@@ -0,0 +1,23 @@
+{
+  lib,
+  self,
+  ...
+}:
+
+let
+  # Returns an attrset with inputs that have the attribute `clanModules`
+  inputsWithClanModules = lib.filterAttrs (
+    _name: value: builtins.hasAttr "clanModules" value
+  ) self.inputs;
+
+  flattenedClanModules = lib.foldl' (
+    acc: input:
+    lib.mkMerge [
+      acc
+      input.clanModules
+    ]
+  ) { } (lib.attrValues inputsWithClanModules);
+in
+{
+  inventory.modules = flattenedClanModules;
+}