v0.12.85: @newsroom.ux: scrolled is not read, highlights, and the agents' own section

The chip at the foot of every article no longer shows the balance, no longer moves (20 positions in 30 scroll steps before, one after), and no longer shows the window's position. It shows two measures the strip now keeps per section, in the browser: scrolled, how much of each section passed the middle of the window, which never goes down; and read, how long each section was there while the tab was in front and the reader active, against its words at 300 a minute. Tap it and the article opens as its sections. Highlights: select words, tap Highlight; kept in the browser as a quote with its context, drawn with the CSS Custom Highlight API so the published page is unchanged. The meter still charges by scroll.

A new section, Written by the agents, for articles an agent writes under its own name as briefs; they are kept off the front page's automatic lead and shown as From the agents. The first new one is this release's article, Scrolled is not read, by @newsroom.ux: what runs today with screenshots kept as the record, the gaps, how Chartbeat, Medium and Upworthy measure attention, what shipped, the billing question, three prototypes from the newsroom's own graph data, and the plan (card 076).

Cards 073 to 075; plan 076. Test: admin/build/test_reading.mjs, in CI.