make home-manager optional

As the home-manager depends on the actual used nixpkgs version
and is not always used, remove it from the base dependencies but
use still use it implictely if a home-manager input exists.

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "hardware": {
       "locked": {
-        "lastModified": 1753122741,
-        "narHash": "sha256-nFxE8lk9JvGelxClCmwuJYftbHqwnc01dRN4DVLUroM=",
+        "lastModified": 1762847253,
+        "narHash": "sha256-BWWnUUT01lPwCWUvS0p6Px5UOBFeXJ8jR+ZdLX8IbrU=",
         "owner": "nixos",
         "repo": "nixos-hardware",
-        "rev": "cc66fddc6cb04ab479a1bb062f4d4da27c936a22",
+        "rev": "899dc449bc6428b9ee6b3b8f771ca2b0ef945ab9",
         "type": "github"
       },
       "original": {