flake: use nix-openclaw fork with plugin manifest fix

Temporary fork until PR #81 is merged upstream:
openclaw/nix-openclaw#81

Author: ivankovnatsky

flake.lock

@@ -264,7 +264,9 @@
     };
 
     nix-openclaw = {
-      url = "github:openclaw/nix-openclaw";
+      # FIXME: using fork with plugin manifest fix until PR #81 is merged
+      # https://github.com/openclaw/nix-openclaw/pull/81
+      url = "github:bobberb/nix-openclaw/fix/copy-plugin-manifests";
     };
   };