Fix blue palette table link contrast

[sean-camara]

What this PR does

Keeps links legible when a light table is rendered inside the blue palette. Tables now own the link color variables appropriate to their fixed surface: dark text and underline colors for light tables, and the existing light treatment for dark tables.

The root cause was that links inherited white text from the surrounding blue palette even though the table itself intentionally renders on a white surface, producing 1:1 contrast.

Closes #146

Type of change

• Bug fix (patch)
• New feature or component (minor)
• Breaking change (see Public API section below)
• Documentation only
• Tooling or CI (no effect on published output)

Checklist

• npm run format:fix and npm run lint:scss:fix pass
• npm run lint:js and npm run lint:md pass
• Tested across all 6 palettes in Storybook
• Tested across mobile, tablet, and desktop viewports
• Automated a11y checks pass (npm test)
• Storybook documentation updated (if component changed)

Public API and changesets

• Ran npm run check:api-snapshot and reviewed the result
• Changeset added with a patch bump
• Bump level matches the semver rubric

Visual review

The new Components/Table/Links on blue palette regression story renders the interactive table on the blue palette and verifies that link text uses the table cell's dark foreground color. Existing palette accessibility stories continue to exercise all six palettes.

Notes for reviewers

Validation completed locally:

• npm run build
• npm test (241 tests)
• npm run lint
• npm run format:fix
• npm run lint:scss:fix
• npm run check:api-snapshot
• npm run check:tokens

[sean-camara]

Hi @abbybowman, just following up on this PR when you have a chance. The code checks are passing, but the Chromatic visual regression check is currently blocked by a missing project token in the repository configuration. I’d appreciate your review, and please let me know if any changes are needed. Thank you!

[abbybowman]

Thanks again for this @sean-camara! A few changes requested below

[abbybowman]

I think we can skip this one. The existing PaletteA11y story already renders AllVariants (which includes interactiveTable with real links) across all six palettes including blue, so the surface your fix targets is already exercised there and will reflect this fix (see screenshot below from Chromatic). We have a limited Chromatic snapshot budget on the free plan so trying to leverage our existing Stories whenever possible, just like you did in #149!

[abbybowman]

I'd drop these three lines. On the dark and black palettes the ancestor palette already supplies the correct dark link vars, and the table's dark surface (Carbon 90) is the same as the dark palette background, so this block re-declares values that are already right.

It also drifts slightly: --hds-palette-link-arrow is set to Carbon 30 here, but our dark scheme uses Carbon 40 (_palettes.scss:106). So this actually introduces a small inconsistency (see Chromatic screenshot below).

I think the base .usa-table block is all that's needed to fix the blue bug, but if you'd recommend keeping an explicit dark block for self-documentation, that would make sense to me too; let's just match the scheme exactly (arrow → Carbon 40).

Thank you, will look out for your updated PR and get it turned around more quickly, sorry this review took a bit -- greatly appreciate you jumping in to help fix these bugs!

[abbybowman]

I know main changed underneath you, so just a note to update this line to match our final NPM package name: '@nasa-hds/core': patch