Fix flake output schema and devShell wiring causing CI flake-check failures

[Copilot]

• Inspect latest Validate Flake failure logs for the current branch
• Identify the concrete failing expression behind homeConfigurations.c0d3h01
• Replace unsafe config.services.*Desktop.enable lookups with safe defaults in Home Manager gtk module
• Re-scan home modules for similar unsafe attribute access patterns
• Validate via CI-oriented checks where possible and summarize results

[Copilot]

Pull request overview

This PR fixes flake output shape and module evaluation issues that were causing nix flake check/CI validation failures, particularly around homeConfigurations.c0d3h01 and Home Manager module evaluation outside NixOS.

Changes:

• Fix flake output schema by defining nixosConfigurations.c0d3h01 and homeConfigurations.c0d3h01 directly (not nested per-system), and wire specialArgs/extraSpecialArgs consistently.
• Make modules/home/gtk.nix safe under standalone Home Manager evaluation by guarding optional config.services.* lookups with defaults.
• Fix devShells import wiring by passing pkgs correctly and providing formatter to shell.nix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
modules/home/home.nix	Sets a concrete home.username to avoid problematic self-referential evaluation in standalone HM configs.
modules/home/gtk.nix	Replaces unsafe config.services.*.enable reads with lib.attrByPath defaults for standalone HM compatibility.
flake.nix	Corrects output schema for nixosConfigurations/homeConfigurations, adds consistent specialArgs, and fixes devShell/formatter plumbing.