Opt-in automatic spacing layer (zero-specificity gaps)

[jackgranatowski]

Problem

Spacing today is applied through explicit primitives (.sf-stack, .sf-grid, .sf-flow, .sf-prose). Some users want default gaps applied automatically without adding classes. We have no opt-in "automatic spacing" layer.

Scope

• An opt-in module applying container/content gaps with zero specificity (e.g. :where(.sf-section > *), :where(.sf-grid-*)) so any explicit class/inline style overrides trivially.
• Must not change default behaviour when not enabled; document the trade-offs vs explicit primitives.

Acceptance

• Opt-in auto-gap module, zero-specificity, easily overridden
• Off by default; documented