feat(dashboard): add unified model catalog page

[Dattuog]

Summary

• Add /dashboard/models and an OmniProxy sidebar link to browse models from every provider.
• Reuse GET /api/models/catalog; show model ID, type, capabilities, context, output limit and reported free/custom flags in a sortable table with search, filters, paging, refresh and failure states.
• Keep missing metadata visibly unknown rather than implying a model is paid or lacks a capability.

Related Issues

Closes #12593.

⚠️ base-red inherited: #14547. The independent release repair is #14683; this feature branch does not include those changes.

Validation

• Change type: UI
• Focused Vitest tests and sidebar Node tests
• Scoped ESLint and Prettier
• Reconciled with current release tip 18bbb1019
• Production-code changes include automated tests
• npm run lint on this branch: inherited stale suppression entries; resolved separately in [dup] fix(quality): restore release typechecks and env-doc sync #14683

npx vitest run --config vitest.config.ts tests/unit/dashboard/modelCatalogPage.test.tsx tests/unit/dashboard/modelCatalogUtils.test.tsx
  Test Files  2 passed (2)
  Tests       10 passed (10)
node --import tsx --test tests/unit/sidebar-visibility.test.ts
  tests 8; pass 8; fail 0
npm run test:vitest
  Test Files 51 passed (51); Tests 482 passed (482)
GET /dashboard/models           HTTP 200
GET /api/models/catalog          HTTP 200

Tests Added Or Updated

• tests/unit/dashboard/modelCatalogPage.test.tsx
• tests/unit/dashboard/modelCatalogUtils.test.tsx
• tests/unit/sidebar-visibility.test.ts

Coverage Notes

The page test covers catalog loading, rendering, filtering, sort controls and request failure. Utility tests cover flattening, search, sorting and page bounds. Sidebar tests cover discovery and visibility.

Reviewer Notes

No migrations or new backend aggregation. The current catalog endpoint omits some metadata for some providers, and the UI shows a dash for those fields. Local full UI Vitest had unrelated pre-existing failures; PR CI will provide the authoritative run. Core and dashboard typecheck errors on the release tip are addressed in #14683.

[diegosouzapw]

Clean, small feature that fills a real gap (there was no cross-provider catalog view). Ran
your test files locally: 10/10 pass, and the sidebar-fallback pattern you used means no i18n
keys were needed — nice. Only thing missing before merge: a changelog fragment under
changelog.d/features/ (see changelog.d/README.md for the convention). Everything else
looks merge-ready to me.

[Dattuog]

Thanks for the review and for running the focused tests. I added the requested feature changelog fragment in 96ab034, following the convention in changelog.d/README.md.