fix(home-manager): resolve infinite recursion in imports.nix

Move isDarwin evaluation from top-level let binding into the config
section to avoid infinite recursion when evaluating standalone
home-manager configurations.

The issue occurred because:
1. isDarwin = pkgs.stdenv.hostPlatform.isDarwin was evaluated early
2. This required pkgs to be fully evaluated
3. pkgs evaluation required config evaluation
4. config evaluation required foreground.enable
5. foreground.enable tried to use isDarwin
6. Infinite loop

Fix: Inline the pkgs.stdenv.hostPlatform.isDarwin check directly in
the config section where it's used, allowing lazy evaluation.

This fixes the GitHub Actions error:
  error: infinite recursion encountered
  while evaluating packages.x86_64-linux.static-home

Author: arunoruto

modules/home-manager/imports.nix

@@ -5,7 +5,6 @@
   ...
 }@args:
 let
-  isDarwin = pkgs.stdenv.hostPlatform.isDarwin;
   # Check if we're on NixOS (osConfig.system.tags exists)
   isNixOS = args ? osConfig && osConfig ? system && osConfig.system ? tags;
 in
@@ -51,7 +50,7 @@ in
     # Darwin and NixOS common configuration
     (lib.mkIf (args ? osConfig) {
       foreground.enable = lib.mkDefault (
-        if isDarwin then
+        if pkgs.stdenv.hostPlatform.isDarwin then
           true # Always enable on Darwin
         else
           osConfig.programs.enable # Use NixOS custom option