Refresh homepage, docs layout, and branding

[osiewicz]

Summary

• Replace the homepage with the compact two-column layout, controllable scenario examples, focused Get started action, contact links, and a restrained footer.
• Surface the newest non-draft blog post automatically, using its existing title, summary, and date.
• Apply the mineral light/dark palette, gray cut-W mark, updated icons/social preview, and self-hosted Source Sans 3, Barlow Semi Condensed, and JetBrains Mono fonts.
• Tighten docs typography, spacing, header alignment, sidebar selection, and mobile navigation; keep search available on mobile.
• Update introduction, installation, and quickstart docs to explain local CLI measurements and the path into the app.

Verification

• npm run build passes (15 pages).
• Whitespace check passes excluding unchanged upstream formatting in vendored font licenses.
• Checked the homepage and docs at desktop and mobile widths in light and dark themes.
• Verified the blog link, mobile docs menu/search, and automatic newest-post selection, including draft-only and empty collections.

Remaining Review

• Unfinished docs remain listed and accessible; this PR does not hide them.
• Hosted app onboarding has not been exercised end to end.
• Local builds use the existing author-name fallback when the GitHub avatar lookup is unavailable.