[HEIHEI-928] fix: infer columnheader/rowheader for th without scope

[bbrzoska]

Refs vitest-dev/vitest#8054

Problem

getByRole('columnheader') and getByRole('rowheader') in Vitest browser mode don't find a <th> that has no scope attribute. ivya treats such a th as a cell, which is how Playwright behaved when #8054 was closed. Playwright has since changed the rule in microsoft/playwright#38160 (released in 1.57), so for the same markup Playwright's page.getByRole('columnheader') now finds the header cells and Vitest's doesn't.

Change

This ports Playwright's current TH rule from packages/injected/src/roleUtils.ts into src/roleUtils.ts, including the two helpers isHeaderCell and isNonEmptyDataCell:

• An explicit scope still wins: col/colgroup gives columnheader, and row/rowgroup gives rowheader. colgroup and rowgroup weren't recognised before.
• Otherwise the role comes from the neighbouring cells, as Chromium does it (ax_node_object.cc). A th with a non-empty td next to it is a rowheader. Any other th is a columnheader. The one exception is a lone th in a single-row table, which gets no role.

Tests

test/role.test.ts runs on chromium, firefox and webkit. It covers these cases, taken from the ones Playwright added in #38160:

• a header-row th is a columnheader, with or without thead
• a th first in a body row is a rowheader
• a th next to an empty td is a columnheader
• a lone th in a single-row table has no role, and in a multi-row table it's a columnheader
• all four scope values beat the position-based rule
• the table from #8054 works end to end through queryAllByRole and getByRoleSelector

Nine of these fail without the change. The table structure roles aria snapshot now shows columnheader "H" where it used to show cell "H", which is what Playwright's snapshot shows.

I also checked every fixture outside the test suite with Playwright 1.60 on Chromium. For each one I compared ivya's new result with Playwright's page.getByRole and with Chromium's accessibility tree from CDP Accessibility.getPartialAXTree. They matched in all eight cases, including the lone th (Playwright gives no role, and Chromium reports a layout-only LayoutTableCell).

Once this is released, Vitest needs its ivya dependency bumped to pick it up.

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