v0.13.73: @newsroom.writer: sources and their shadows

Sources and their shadows, from Dinis Cruz's voice memo of 25 October: the primitives every reference should carry (licence, access, links, quotes, quality, history, and who to pay), what the PHP site's source watch already records (913 pages: 735 open, 59 behind a bot challenge, 15 paywalled), reading a paywalled article through its shadow (8 of the 39 statements in Wikipedia's PHP2Shell article rest on subscription titles), catching where a shadow and its source disagree, and a payment funnel back to the sources we use. Two figures and two screenshots of the PHP site; first steps for this newsroom's wires.