refactor(nix): Use home-manager

Looks like nix-darwin is planning to drop per-user launchd (or perhaps
per-user feature entirely).

.config/nix/flake.lock

@@ -1,5 +1,26 @@
 {
   "nodes": {
+    "home-manager": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1720042825,
+        "narHash": "sha256-A0vrUB6x82/jvf17qPCpxaM+ulJnD8YZwH9Ci0BsAzE=",
+        "owner": "nix-community",
+        "repo": "home-manager",
+        "rev": "e1391fb22e18a36f57e6999c7a9f966dc80ac073",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "ref": "release-24.05",
+        "repo": "home-manager",
+        "type": "github"
+      }
+    },
     "nix-darwin": {
       "inputs": {
         "nixpkgs": [
@@ -38,6 +59,7 @@
     },
     "root": {
       "inputs": {
+        "home-manager": "home-manager",
         "nix-darwin": "nix-darwin",
         "nixpkgs": "nixpkgs"
       }