fix(data-table): strengthen row hover contrast

[kirillDevPro]

Summary

• route MoonDataTable row hover through the shared semantic table_hover role
• remove the weakened 28% local palette override
• add a regression contract for the theme-role wiring

Validation

• powershell -ExecutionPolicy Bypass -File tools\run-component-guardrails.ps1
• mutation proof: green -> old 0.28 hover -> red -> restore -> green
• downstream cargo test --workspace with local three-crate MoonUI patch
• downstream cargo clippy --workspace --all-targets