fix(core): preserve layer frame borders by insetting content

[RtlZeroMemory]

Summary

Fixes layer frame border rendering so child content no longer overwrites border cells.

Changes

• Inset layer content layout by 1 cell on all sides when a valid frameStyle.border is set.
• Clip layer child rendering to the same inner rect when border is enabled.
• Added regression coverage:
  • layout test asserting inset child rect
  • renderer regression test asserting inner clip command

Validation

• npm run lint
• npm run typecheck
• npm run build
• node --test --test-concurrency=1 packages/core/dist/layout/__tests__/layout.edgecases.test.js packages/core/dist/widgets/__tests__/renderer.regressions.test.js