data: add docs links for 12 products; un-discontinue MediaSignage

[514sid]

What

Documentation review of the 23 recently added products, plus a status fix.

Set has_docs: true with a verified docs_url on the 12 that have real public
documentation (knowledge base, help center, or a proper user guide, not a bare
FAQ):

aiscreen, brix, dynasign, menuboard-manager, niio-art, screenbird, seed-signage,
signos, taplist, tecastic, untappd-for-business, vmcast.

The other 11 have no qualifying public docs and stay has_docs: false
(actionfigure, dsmenu, eye-in-media, onsignage, pixage, qsrsoft-tv,
right-media-solutions, screen-pulse, signstream, signjet, tsn). Several offer
only an FAQ, a contact form, or a login-gated portal, none of which count.

Also flips MediaSignage back to discontinued: false; the product (Hughes cloud
digital signage) is active.

Notes for review

• menuboard-manager: knowledge base is hosted at menumagik.ai/kb (a related brand
  domain), rendered client-side.
• signos: docs are per-platform install guides linked from the homepage
  downloads section, so the URL is an anchor.

Validation

bun run check passes on all 624 products.