Skill Labs got a real visual redesign

Skill Labs (still an early preview — these exercises haven't been through practitioner review yet) got a full visual pass:

- A real card grid on the catalog page, with a distinct color per exercise type - The brief (goal, scenario, audience, constraints, deliverable, rubric...) is now laid out as clear, scannable fields instead of one long stacked block - A proper workspace for your own submission, with a clear status indicator - Fixed: the resources listed on a lab (articles, references) weren't showing up at all before — they are now