[dashboard-components] Refactor table-region built-in inventory tables

Summary

Extracted the remaining repeated built-in inventory table wrapper markup in pages/dashboard/src/presenter.js into the existing reusable renderTableRegion(...) component.

Duplication evidence

Repeated .table-region > table > thead > tr > th* plus tbody empty-row construction remained at these call sites in pages/dashboard/src/presenter.js before this refactor:

renderEnginesModelsPage
renderOperationalValuePage
renderOrganizationsPage
renderRepositoriesPage
renderExperimentsPage
renderGradersPage
renderEvalsPage

Each site repeated the same table-region wrapper shape and differed only in table class name, header labels, empty-state message, column span, and row renderer.

Call sites collapsed

Reused pages/dashboard/src/components/table-region.js at every duplicated call site identified above, including both grader tables and both eval tables.

Tests added

Expanded pages/dashboard/test/unit/table-region.test.js
- added keyed-list descriptor coverage for populated body rows used by built-in presenter tables

Behavior preservation evidence

Kept all existing DOM text, accessible names, class names, and empty-state messages unchanged.
Verified the presenter diff is limited to replacing duplicated wrapper construction with renderTableRegion(...) calls.
Full suite remained green after the refactor.

Gates

Ran from pages/dashboard/:

npm install ✅
npm run typecheck ✅
npm run lint ✅
npm test ✅
npm run test:e2e ✅

Blockers

None.

Next candidates

Extract repeated custom-view source/metadata/context chrome.
Extract repeated provenance section rendering for built-in pages.
Extract repeated built-in page section headings plus inventory-table composition once the remaining table call sites settle.

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