WIDGETS: fourteen widget tools built from .t27 specs #1378

Part of #1377.

Problem

The WIDGETS gallery lists seven ideas as "not built yet" and has no way to host a tool that runs in the page.

Change

• specs/widgets/<id>.t27 (KIND widget-tool) + scripts/widget-pages-from-spec.mjs write public/widgets/<id>/index.html with og/twitter cards, window.T27_WIDGET, and a t27:hook meta the gallery reads.
• Fourteen tools: bit-diff, test-waves, gf16-calc, race-the-bee, placement-map, resource-bars, slack-waterfall, idcode, pin-map, cost-curves, lut-explain, build-receipt, gatle, test-touch.
• gallery.t27: tools listed as kind tool; the idea list is refilled with ideas not built yet.
• CI: check:widget-pages + test:widget-pages in Website checks.

Acceptance

• Every page is current (--check), has a 1200x630 card, and every spec's tests pass.
• Gallery shows each tool with its own hook.