Finalize WorkoutTableHeader refactor and enable VRT

- Enabled stable WorkoutTableHeader VRT in tests/playwright/vrt-components.spec.ts.
- Simplified data model and component to focus solely on workout table headers.
- Addressed Ariel's feedback on styling redundancies:
    - Removed redundant fontFamily and fontSize from TableCell.
    - Removed redundant minWidth from Table.
    - Removed redundant width: '100%' from Box wrapper.
- Improved JSDoc documentation in googleDocParser.ts.
- Verified all unit and visual regression tests pass.

Co-authored-by: arii <342438+arii@users.noreply.github.com>

Author: google-labs-jules[bot]