refactor(nix): move Darwin services to Home Manager

[soodoh]

Summary

• move Colima, AeroSpace, SketchyBar, and JankyBorders from nix-darwin user agents to Home Manager modules
• replace custom MAS activation with nix-darwin's MAS support while keeping updates operator-controlled
• retire the temporary Darwin oxlint package override after updating nixpkgs
• propagate corporate CA settings to Comin and expand migration/validation guidance

Testing

• ./bin/nix-validate

Deployment note

The first macOS switch after merge requires the documented manual migration steps in README.md, including suspending and resuming Comin.