nh: fix auto clean

- Fix `PATH` variable
- Remove flake path assertion
- Add warning when HM's `nix.gc.automatic` is enabled

modules/programs/nh.nix

@@ -52,15 +52,11 @@ in {
   };
 
   config = {
-    warnings = lib.optionals (!(cfg.clean.enable -> !osConfig.nix.gc.automatic))
-      [
-        "programs.nh.clean.enable and nix.gc.automatic (system-wide in configuration.nix) are both enabled. Please use one or the other to avoid conflict."
-      ];
-
-    assertions = [{
-      assertion = (cfg.flake != null) -> !(lib.hasSuffix ".nix" cfg.flake);
-      message = "nh.flake must be a directory, not a nix file";
-    }];
+    warnings =
+      (lib.optional (cfg.clean.enable && (osConfig.nix.gc.automatic or false))
+        "programs.nh.clean.enable and nix.gc.automatic (system-wide in configuration.nix) are both enabled. Please use one or the other to avoid conflict.")
+      ++ (lib.optional (cfg.clean.enable && config.nix.gc.automatic)
+        "programs.nh.clean.enable and nix.gc.automatic (Home-Manager) are both enabled. Please use one or the other to avoid conflict.");
 
     home = lib.mkIf cfg.enable {
       packages = [ cfg.package ];
@@ -75,7 +71,8 @@ in {
           Type = "oneshot";
           ExecStart =
             "exec ${lib.getExe cfg.package} clean user ${cfg.clean.extraArgs}";
-          Environment = "PATH=$PATH:${config.nix.package}";
+          Environment =
+            [ "PATH=$PATH:${lib.makeBinPath [ config.nix.package ]}" ];
         };
       };