feat: add Competency Tree on the Competency Management page

[AShatsila]

Description

Adds a new read-only Competency Management page at /taxonomy/:taxonomyId/competencies. It shows a competency taxonomy's tags as a nested expand/collapse tree (taxonomy name → groups → sub-competencies), with each row's Competency ID (external_id) displayed next to it. The page is fully read-only: no editing of names or IDs, no add/edit/delete affordances anywhere, and no backend/API/data-layer changes.

This is a new page, so it doesn't change behavior for any existing role. It's intended for Platform Administrators who need to browse a taxonomy's competencies by their stable Competency ID before applying competency criteria elsewhere.

Supporting information

• Closes [FE] Display Competency ID on the Competency Management page openedx-core#680
• Figma design

Testing instructions

1. Enable the ENABLE_TAGGING_TAXONOMY_PAGES feature flag.
2. Have (or create) a competency taxonomy with a nested tag tree at least 2 levels deep, where at least one tag has no external_id set.
3. As a Platform Administrator (staff) user, navigate to /taxonomy/:taxonomyId/competencies for that taxonomy.
4. Confirm the tree renders with the taxonomy's own name as the top row, groups below it, and sub-competencies nested under their group.
5. Use Expand All / Collapse All and individual row toggles; confirm indentation stays correct at every level.
6. Confirm each tag with an external_id shows it as a badge, and the tag without one shows no badge (not the literal text "undefined" or "null").
7. Confirm there is no add/edit/delete/rename control anywhere on the page.
8. Resize to a narrow viewport and confirm the tree and Competency IDs stay readable and correctly associated.
9. Open the existing /taxonomy/:taxonomyId page (tag editing) and confirm it's unaffected — same table, same columns, same zebra striping as before.

Other information

• No backend, API, or data-layer changes.
• Entry point is URL-only for this ticket — no link was added from the taxonomy detail page or its menu, per the agreed scope.
• The API doesn't distinguish "competency" taxonomies from other taxonomies, so this page will render whatever taxonomy id is in the URL, including system-defined ones whose tags may not be fully enumerable. Known limitation, to revisit once/if the backend exposes a competency-enabled flag.
• Architecture note: this page does not reuse the existing table-based tag tree-table shell (src/taxonomy/tree-table/) that the editable taxonomy detail page uses. That shell is built around an HTML <table>/TanStack Table, which can't express per-row gaps or nested "card" grouping without hacky workarounds (<tr> can't take margin, and a box-shadow-based border approach bled across row boundaries). Since this page needs neither the shared shell's editing machinery nor its tabular semantics, it renders its own lightweight <ul>/<li> tree instead, reusing only the taxonomy-tag-to-tree data shaping (TagTree) from the existing tag-list feature.
• Paragon note: the Competency ID badge's exact color (#006DAA) doesn't correspond to any existing Paragon semantic color variant in this app's theme (variant="info" resolves to teal) - it's retinted via a page-scoped CSS custom-property override on top of the real Badge component. Flagging per the standing internal reminder to surface anything not natively available in Paragon.
• Accessibility: the disclosure chevron's clickable area is kept at the WCAG 2.2 AA minimum of 24×24px even though its visible icon is smaller (16px, per the Figma spec), via an invisible expanded hit area. The Competency ID badge also carries its own aria-label since there's no table header for screen readers to associate it with.

Best Practices Checklist

• Any new files are using TypeScript (.ts, .tsx).

• Avoid propTypes and defaultProps in any new or modified code.

• Tests should use the helpers in src/testUtils.tsx (specifically initializeMocks)

• Do not add new fields to the Redux state/store. Use React Context to share state among multiple components.

• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.

• All new i18n messages in messages.ts files have a description for translators to use.

• Avoid using ../ in import paths. To import from parent folders, use @src.

• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

• Any new files are using TypeScript (.ts, .tsx).
• Avoid propTypes and defaultProps in any new or modified code.
• Tests should use the helpers in src/testUtils.tsx (specifically initializeMocks)
• Do not add new fields to the Redux state/store. Use React Context to share state among multiple components.
• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.
• All new i18n messages in messages.ts files have a description for translators to use.
• Avoid using ../ in import paths. To import from parent folders, use @src, e.g. import { initializeMocks } from '@src/testUtils'; instead of from '../../../../testUtils'

[openedx-webhooks]

Thanks for the pull request, @AShatsila!

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