Function
This is the page's one client island. It reads the three device stores —
completion marks, playback positions and the continue-watching record — once,
and derives every tile from a single courseOverviewProgress reading so no two
tiles can disagree.
Until the page has hydrated and the record has been read, every tile renders
its pending shape. On a phone the course tile comes first, then the continue
tile and one row per lesson; from lg the continue tile spans two thirds
beside the course tile, and lessons sit five to a row.
The course overview's progress board: the continue tile and the course progress tile, which leads to the course page, then one ring tile per lesson.