Refactor and Update Templates

[erikreinert]

Added

• mkLanguage, mkDarwin, mkHomeManager, mkNixosDesktop, mkNixosMinimal functions

Removed

• Direct template commands in lib/default.nix

Changed

• Updated flake.lock with new revisions
• Refactored flake.nix and lib/default.nix for better modularity
• Moved Zig section in README.md
• Updated README.md formatting and instructions

[hbjydev]

@erikreinert Don't we already have a NestJS template?

[hbjydev]

Oh, nvm, I see the issue.