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

@@ -15,27 +15,6 @@
         "type": "github"
       }
     },
-    "home-manager": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1747688870,
-        "narHash": "sha256-ypL9WAZfmJr5V70jEVzqGjjQzF0uCkz+AFQF7n9NmNc=",
-        "owner": "nix-community",
-        "repo": "home-manager",
-        "rev": "d5f1f641b289553927b3801580598d200a501863",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-community",
-        "ref": "release-24.11",
-        "repo": "home-manager",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1751274312,
@@ -55,7 +34,6 @@
     "root": {
       "inputs": {
         "hardware": "hardware",
-        "home-manager": "home-manager",
         "nixpkgs": "nixpkgs"
       }
     }