0.9.0

Site: stack label/value rows on phones, add robots.txt and sitemap.xml

A long asset filename in the download cards wrapped to two right-aligned lines
under its label at 375px, which read as ragged. The label/value rows now stack
on narrow screens, which fits "Cadence-Animator-Setup-0.8.0.exe" on one line.

Verified alongside the rest of the site by driving it in a real browser: nav
active-state at every section, the mobile hamburger (including aria-expanded and
close-on-tap), the shortcut filter and its empty state, FAQ disclosure, the
injected copy buttons and the skip link — 21/21.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>