[P2.78] Launch page: extend the one-page site with the demo, install command and sample export #1476

Launch runbook 5.4. An upgrade of #1465, not a second site.

Depends on #1474, #1472 and #1471.

Gated on the owner for three inputs: final copy, the product mark, and name clearance for the product branding. Do not put the product name on the page before the owner confirms clearance.

• Above the fold: the 45-second demo, one install command, one call to action.
• Below: the three proof points, a sample evidence export, and the limitations section verbatim.
• The contact call to action becomes the install command.