feat(webkit): add the card-grid marketing component

[gabriel-lisboa-azion]

Summary

• The responsive cell grid of the page language, in three registers: spaced cards separated by real gutters, a hairline box grid whose internal rules are the gaps themselves, and a framed grid whose cells are real frame-box elements. The frame register is the one that composes: each CardGrid.Cell draws its own rules and corner marks and carries its own fill, so the grid needs no background trick and nests flush inside a column that already owns the outer edges.
• Public exports: @aziontech/webkit/card-grid, @aziontech/webkit/card-grid-root, @aziontech/webkit/card-grid-cell.

How to test

1. pnpm storybook:dev → open Components/Marketing/CardGrid. Every story renders, and "Show code" is a runnable SFC you can paste.
2. pnpm --filter @aziontech/webkit test -- src/components/marketing/card-grid → the co-located browser suite passes.
3. pnpm webkit:type-check → clean.

Notes

• No dependency on another marketing PR; it can merge in any order.
• Targets feature/marketing-components, which carries the shared foundation (marketing category registration, illustration scene registry, theme tokens, story assets).
• No breaking change: nothing is removed or renamed on main.