Convert course-home tab data to React Query

Why a query, not lifted state

The Redux field is a hand-rolled loading flag for one fetch. The tab conversions already replaced such flags (courseStatus strings) with query state, so the same move applies: make the fetch a query and read isPending off it. Both readers call the hook; React Query dedupes by key; no new context or lifted useState.

Pieces

1. course-home/data/queryKeys.ts + apiHooks.ts — proctoringInfo(courseId, username) key; useProctoringInfoData(courseId, username, enabled = true) wrapping the unchanged getProctoringInfoData (its 404 → {} mapping stays in the api).
2. ProctoringInfoPanel.jsx — replace the mount effect + six useStates with the query and plain derivation from data (status, link, expiry → readable status, release date, past-due, show-panel = non-empty response). The response is raw snake_case today; keep the reads or camelCase in the hook — same rendered output either way. useDispatch, the slice import, and the exhaustive-deps disable leave.
3. OutlineTab.jsx — (!enableProctoredExams || proctoringPanelStatus === 'loaded') → (!enableProctoredExams || !isPending) from the same hook (username already in scope from courseHomeMeta).
4. ProductTours.jsx — same hook with enabled: outlineTabActive (the panel only ever mounted on the outline tab, so no new request elsewhere). Username must be the courseHomeMeta one the panel keys on (masquerade-aware), not getAuthenticatedUser().username, or the query key forks under masquerade — LoadedTabPage already reads courseHomeMeta and passes it as a prop (revisit at code review).
5. Delete slice.js, course-home/data/index.js; drop courseHome from store.ts and initializeTestStore. Check whether LOADED in constants.ts loses its last importer.

Settled-vs-error (decided: !isPending + retry: false)

The panel's .catch(() => {}) and .finally(resolve) were added together in PR #727 (2021) so the goals widget would never stay hidden because of this request — settling on any outcome is the intent. The catch's "API throws 404" comment was already wrong when written (the api had mapped 404 → {} since the panel's first commits), and before #727 a 5xx surfaced as an unhandled rejection, so silencing real failures was a side effect, not a choice. The query keeps the intent and drops the accident: readers gate on !isPending (never isSuccess); retry: false so a failure settles immediately as #727 designed rather than after the app default's ~7s of 5xx retries; no swallow in queryFn, so the error reaches the app QueryCache.onError and is logged. Rendered output on error is unchanged (no data → panel hidden).

Tests

• apiHooks.test.tsx: payload resolves; 404 → {}; enabled: false idle; non-404 → isError.
• OutlineTab.test.jsx: the existing proctoring block renders the panel against a mocked endpoint and should pass unchanged; add a weekly-goal-deferral case if none asserts the gate today.
• ProductTours.test.jsx: already mocks the proctoring URL (404) so the outline tour proceeds; passes once the hook keys on the same username the mock uses.

Commit

refactor: retire the courseHome Redux slice — Closes #1975. Not breaking: proctoringPanelStatus was never a documented or plugin-facing surface.

After this layer

Stack #2062 layer 16. Then #2017 (plugins reducer) and #1977 (models reducer), leaving store.ts at specialExams only — #1978's endpoint.