Cap wizard option lists at 60vh and scroll

[Copilot]

Long option lists (agent engine, triggers, outputs, extras) grew unbounded and pushed the rest of the wizard below the fold.

Changes

• .option-group now has max-height: 60vh with overflow-y: auto, plus padding-right and scrollbar-gutter: stable so hover shadows and the scrollbar don't shift card layout.
• .option-group.archetype-grid drops its bespoke 32rem cap and scroll rules, inheriting the shared behavior; it keeps only its grid layout.

.option-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  max-height: 60vh;
  overflow-y: auto;
  padding-right: 0.25rem;
  scrollbar-gutter: stable;
}