Group Guide TOC and sync URL hash on click

[PunchTheDev]

Summary

Re-rubric pass on Guide TOC against the 3 pillars. Groups the flat 12-item nav into Concepts · Onboarding · Reference so a first-timer sees the onboarding arc at a glance, adds per-item hover previews, and fixes the silent deep-link bug.

Teardown

• Beautiful: flat 12-item list, no grouping; first-timer can't tell which items form the Steps 1–5 arc vs concept primers vs deeper reference.
• Seamless: clicks called preventDefault + scrollIntoView but never updated the URL hash → refresh/back-button/share-link all lost the position. Modifier keys (cmd/ctrl-click) couldn't open a section in a new tab.
• Understandable instantly: hover gave no preview of what's in each section.

Changes

• QuickstartGuide.tsx L271–425: replace TOC_ITEMS flat array with TOC_GROUPS (Concepts · Onboarding · Reference) → TocItem carries a preview string used as title= tooltip (113–134 chars each).
• Click handler now history.replaceStates the URL hash so refresh + back-button + share-link all round-trip. Honors metaKey/ctrlKey/shiftKey/altKey so cmd/ctrl-click opens in a new tab via the browser default.
• IntersectionObserver scroll-spy and indent flag for Step 3 sub-items preserved verbatim.

Verification

Puppeteer 1440×900 on /guide:

• groupHeadings: ["Concepts","Onboarding","Reference"], itemCount: 12
• Click on API reference → URL updates to /guide#api
• Direct load /guide#rewards → scrollY=6000, scroll-spy marks How rewards work active
• All 12 tooltips present (113–134 chars)
• 0 new console errors (1 pre-existing 404 unchanged)