Rebuild Explorer Quick Start with prereqs and 5 canonical steps

[PunchTheDev]

Summary

Explorer's Quick Start was a 4-step recipe in the wrong order (install → scaffold → eval → then explore) with no prereqs row and no PR-submission step. Rebuilt as 5 steps in onboarding-arc order (install → explore → scaffold → eval → PR), with prereqs surfaced explicitly and every step header routed to the canonical Guide section.

Changes

• Playground.tsx L83–203 — QuickStartBlock rewritten:
  • Prereqs strip (Docker Desktop + Python 3.11+) added above the code block as cursor-help tooltips. First-timers without these fail Step 1 silently.
  • Step ordering fixed — "see open problems via API" was Step 4 (after eval); now Step 2 (before scaffold) so the eval command at Step 4 has a chosen spec.
  • Step 5 — open a PR added (was absent). Onboarding loop used to dead-end at "passing eval"; now closes the flywheel with the gh pr create command and a tooltip explaining the passed/optimization CI labels.
  • Routed Guide micro-links — each # N header gets a Step N ↗ link to /guide#setup #explore #write #eval #submit. Explorer's Quick Start now treats itself as the entry point to the canonical explainer, not a duplicate.
  • --docker flag tooltip — explains it's the forge-eval:latest image CI uses, so a local PASS won't surprise you with a CI FAIL (matches step 372 framing).
  • Footer reframed — .forge/results/{selectedSpec}.json parameterized with current spec, mentions the stage field, links to 4-stage pipeline ↗ explainer.
• BACKLOG.md — Explorer Quick Start flipped ○ ○ ○ → ● ● ●.

Verification

Puppeteer 1440×900 on /explorer?spec=r01_001_easy:

• 5 step headings render (# 1. … # 5.)
• 8 routed links: full setup → /guide#setup, Step 1–5 → matching anchors, 4-stage pipeline → /guide#eval, Full Guide → /guide
• 13 tooltips (max 218 chars) including Prereqs row + per-command explainers
• Step 4 click routes /explorer?spec=… → /guide#eval
• Old "see open problems via API" copy gone; 0 new console errors (1 pre-existing 404 unchanged)