home: clear four eval warnings

All pre-existing, all mechanical:

- pointerCursor no longer implies generation from the block alone; set enable.
- top-level elixir_1_18 alias is deprecated for the beamPackages set. Same
  derivation, 1.18.4 either way.
- pkgs.system -> pkgs.stdenv.hostPlatform.system.
- fzf and atuin both bind Ctrl-R. Atuin is sourced last so it already owned the
  key; historyWidget.zsh.command = "" states that explicitly and satisfies
  home-manager's conflict check. Behaviour is unchanged and fzf keeps Ctrl-T
  and Alt-C.

home/common/programs/default.nix

@@ -35,7 +35,7 @@
 
     packages = with pkgs; [
       impala
-      inputs.yogurt.packages.${pkgs.system}.default
+      inputs.yogurt.packages.${pkgs.stdenv.hostPlatform.system}.default
     ];
 
     username = lib.mkDefault "naps62";

home/common/programs/desktop/default.nix

@@ -57,6 +57,8 @@
     ];
 
     pointerCursor = {
+      # setting the block alone no longer implies generation; must be explicit
+      enable = true;
       package = pkgs.numix-cursor-theme;
       name = "Numix-Cursor-Light";
     };

home/common/programs/elixir.nix

@@ -1,6 +1,7 @@
 { pkgs, ... }:
 {
   home.packages = with pkgs; [
-    elixir_1_18
+    # top-level elixir_* aliases are deprecated in favour of the beamPackages sets
+    beamPackages.elixir_1_18
   ];
 }

home/common/programs/zsh.nix

@@ -78,6 +78,10 @@
     fzf = {
       enable = true;
       enableZshIntegration = true;
+      # Both fzf and atuin bind Ctrl-R, and home-manager warns about the clash.
+      # Atuin is sourced last so it already won; this just makes that explicit
+      # and silences the warning. fzf keeps Ctrl-T and Alt-C.
+      historyWidget.zsh.command = "";
     };
 
     zoxide = {