feat: add flake-schemas compatibility

[pcasaretto]

Summary

This PR adds compatibility with flake-schemas by:

• Confirming the existing homeModules.default structure follows flake-schemas conventions
• Adding backwards compatibility for the legacy homeManagerModules naming with deprecation warnings
• Maintaining full functionality while encouraging migration to standard naming

Changes

• Added homeManagerModules.default with deprecation warning that references homeModules.default
• Uses builtins.trace to show warning when legacy naming is accessed

Flake-schemas compatibility verification

Output of nix run github:DeterminateSystems/nix-src/flake-schemas -- flake show .:

├───homeManagerModules
│   └───(unknown flake output)
├───homeModules
│   └───default: Home Manager module

✅ homeModules.default is properly recognized as "Home Manager module"
⚠️ homeManagerModules shows as "(unknown flake output)" - this is expected for the deprecated compatibility layer

Testing

Test flake-schemas compatibility:

nix run github:DeterminateSystems/nix-src/flake-schemas -- flake show .

Test both module access patterns:

# New standard naming (no warnings)
nix eval '.#homeModules.default' >/dev/null 2>&1 && echo "✅ homeModules accessible"

# Legacy naming (shows deprecation warning)
nix eval '.#homeManagerModules.default' 2>&1 | grep -q "WARNING.*deprecated" && echo "✅ Deprecation warning shown"

Test Home Manager integration:

{
  inputs.try.url = "github:tobi/try";
  
  # Either format works:
  home-manager.users.username = {
    imports = [ inputs.try.homeModules.default ];          # ✅ Recommended
    # imports = [ inputs.try.homeManagerModules.default ]; # ⚠️  Deprecated but works
    programs.try.enable = true;
  };
}

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