Restructure home config host/container registration (flakes-6n5b)

Move host/container registration to mixins/home/hosts/ and mixins/home/containers/, update home-configs.nix and activate-home.nix accordingly

Summary of Changes

• Created files for alienware-13, edger, hp-g1, pc (each imports 25.05 version mixin)
• Updated to add 25.05 version import
• Created importing 26.05 version mixin
• Deleted
• Rewrote : removed configDir param, mixinDir now serves both roles
• Rewrote : reads host names from hosts/ and containers/ dirs; fixed fallback key (removed trailing @)
• Removed version imports from configurations/home/yjpark.nix and configurations/home/yj.nix

Verified: nix eval .#homeConfigurations --apply 'x: builtins.attrNames x' returns expected keys.