Redesign landing header for product-site hierarchy

[makefunstuff]

Summary

Implements the header redesign from the design review so the sticky bar reads as product chrome, not a collapsed docs outline.

Changes

• Brand block: wordmark link + sibling WIP chip (WIP no longer nested in the <a>)
• Removed amber .wordmark::after dash
• Wordmark bumped to ~1.05rem / weight 700 so it leads the TOC
• Nav cut to human labels: How it works · Clients · Start · GitHub (dropped See / Not chat / Loop / Cost)
• Header GitHub stays a quiet outline chip; hero primary CTA unchanged
• No mid-width double row: flex-wrap: nowrap; under 720px section links hide, brand + GitHub remain
• Slightly stronger sticky background (0.92)

Files

• site/index.html
• site/styles.css

Test plan

• Desktop: single-row sticky header, wordmark clearly heavier than nav
• Desktop: only How it works / Clients / Start / GitHub in nav; anchors land correctly
• ~700–900px: header does not wrap to two sticky rows
• Mobile (<720px): section links hidden; brand + GitHub remain
• Hero primary GitHub CTA still present

Do not merge until reviewed.