style(web): polish onboarding from the first screen to the top bar checklist - #2015

🟢 Confidence 10/10 · safe to merge. Copy and class changes only, pinned by updated scene tests; the one behavior change (role="alert") is strictly stronger than the removed aria-live.
_{no findings · tests covered · risk low}

A visual polish pass over every onboarding screen, the top-bar credits checklist and the overview setup card, plus two lab preview pages. Only classes, copy and one exported panel function change, apart from the create-org error now using role="alert"; safe to merge.

• optionCard drops accent/checkClassName; selected cards always use border-primary
• Live-step cards become one link each, Back moved beside "Go to {org}"
• checklistPanel exported from shell/onboarding-checklist-view.ts for the lab
• New /lab/onboarding-checklist and ?step=org|region lab routes

_{4c00d6c · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}