Preserve linked CSS layout wrapper styles

[chubes4]

Summary

• Preserve safe linked CSS layout declarations for generic layout wrappers.
• Covers grid/flex wrappers such as hero grids, card grids, rows, stacks, clusters, and columns.
• Add parity fixture coverage for linked CSS-driven layout wrapper styles.

Testing

• composer parity
• git diff --check origin/trunk...HEAD

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode and subagent
• Used for: Visual parity triage, implementation, fixture coverage, and verification.