v0.10.0 — landing scaffold in the spec; the build codes one section folder at a time

Landing pages get a plain scaffold, and the build codes one section folder at a time.

• /pspt:landing-spec gains L4 Scaffold: a plain landing/ folder from templates — index.html, a ten-line Vite inliner, shared/ (tokens, base, a small page.js with stitch, SEAM and handoff) and one sections/NN-name/ folder per section with its own index.html, style.css and script.js.
• /pspt:landing-build now codes one section per run straight into that section's folder. No React, no TypeScript, no tests, no toolchain; each section is checked by eye in the browser, desktop and phone, with its seams at 85/55/25%.

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Full history: CHANGELOG.md