Render HTML in publish modal custom text

[lntutor]

What this PR does / why we need it:

Configured Publish Dataset modal text is now rendered as HTML, matching the configuration intent. The markup is sanitized with DOMPurify before parsing, and component coverage verifies links and line breaks.

Which issue(s) this PR closes:

• Closes Publish Dataset Modal: message is not rendered correctly #1033

Special notes for your reviewer:

The sanitization step prevents configured markup from injecting unsafe content. Chromatic and label-copy checks cannot access fork secrets/permissions; those fork-only failures are expected.

Suggestions on how to test this:

1. Configure publish modal text containing a link and a line break.
2. Open the Publish Dataset modal and confirm both render as HTML.
3. Run the focused PublishDatasetModal component spec; all 14 tests pass locally.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Yes. Configured modal markup now renders as intended; no mockup is required.

Is there a release notes or changelog update needed for this change?:

No separate release note is included.

Additional documentation:

No additional documentation is required.

Verification: focused component tests (14 passing), lint (four pre-existing unrelated warnings), production build, and diff check.

[lntutor]

Merged current develop and resolved the additive changelog conflict on head bd18010482e08f9c87caaec0c5cabb56977c7c19. Relative to current develop, the PR still changes only the changelog, PublishDatasetModal.tsx, and its component spec. Exact-head local verification: focused component spec 14/14 passing, npm run lint passing with four pre-existing unrelated warnings, production build passing, and staged git diff --check passing.

[lntutor]

The fresh GitHub Actions runs for exact head bd18010482e08f9c87caaec0c5cabb56977c7c19 are currently classified as action_required with no jobs, which is a maintainer-controlled fork workflow approval gate rather than a code failure. Could a maintainer approve the workflow run when convenient? The focused test, lint, build, and diff checks are already recorded above.