Release 1.21.0

Browser harness: an unreachable host (ADR-024, roadmap WS-E task 1).

• openPage(…, { block }) makes every request matching a pattern fail, as if the host were down.
• checkUnreachable(url, { block, widths, minText }) loads a page that way (by default with openvibe.network unreachable, where the theme, the frame and sign-in live). It reports whether the page still paints: status 200, settled, real text, a --accent theme token and a background (the body's, or the html's when the body has none). The blocked requests themselves are not counted as errors.
• Tested in headless Chrome: a page whose theme stylesheet is blocked keeps its inline default.

Host's browser-check.js --network-down runs it against every site.