homeModules has no legacy fallback

[caniko]

nixosModules falls back to r.modules for legacy-format repos, but homeModules doesn't:

nixosModules = r.nixosModules or r.modules or {};  # ✅
homeModules = r.homeModules or {};                  # ❌ no modules fallback

This makes HM modules from repos like charmbracelet/nur inaccessible (they land under nixosModules with _class: "nixos" and HM rejects them).

Proposed fix — mirror the existing fallback:

- homeModules = r.homeModules or {};
+ homeModules = r.homeModules or r.modules or {};

Backward-compatible: repos exporting homeModules already hit the first branch. Same pattern could apply to darwinModules/flakeModules for consistency.

Happy to PR if this looks right.