refactor: de-class CoursewareContainer (#2020)

Convert CoursewareContainer from a class + connect component to a functional
component using hooks. Structural only — no data-layer or behavior change: it
dispatches the same thunks and reads the same store. This unblocks the later
courseware React Query peels, which need a function component to call query
hooks a class can't.

- class -> function; connect -> useSelector/useDispatch
- inline the route hooks (useParams/useNavigate/useLocation) and delete the
  withParamsAndNavigation HOC (utils.jsx), its only consumer
- keep the reselect memoize fetch/save guards (held in refs, reading a
  per-render latest ref) inside one no-dependency effect, matching the old
  componentDidMount + componentDidUpdate exactly
- drop the dead previousSequence selector/prop (unused; keep the empty
  previousSequenceHandler that Course still requires)
- guard useIFrameBehavior's activeSequence.unitIds read: removing connect lets
  the global getSequenceId briefly lead the rendered sequenceId prop, so the
  sequence model can transiently be the outline stub (no unitIds)
- drop dead fetchCourseRecommendations{Request,Success,Failure} exports
  (orphaned from the recommendations RQ conversion in #1967)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>