feat(dashboard): replace checklist with next-step card + unified list

Phase 2 Task 41 — Dashboard redesign.

Backend:
- Extend GET /users/onboarding-status with email_verified and shop_setup_done.
- tried_ai_assistant kept in payload for backward-compat during deploy.

Frontend:
- New NextStepCard: surfaces the highest-priority incomplete onboarding item
  with a primary CTA. Priority order: verify email > set up shop > run first
  FlowPilot session > connect PSA > invite teammate > pick a plan (gated on
  trial stage warning/urgent/expired). Returns null when all done OR
  onboarding_dismissed.
- New SetupChecklist: unified single list (no SOLO/TEAM bifurcation), drops
  the stale tried_ai_assistant / Script Builder item, surfaces "Pick a plan"
  when trial stage is warning or later.
- Mounted on QuickStartPage below the hero with a "Show all setup steps"
  toggle. The whole onboarding section auto-hides when there's nothing left
  to nudge on, so the dashboard goes back to clean once setup is done.
- Removed the orphaned OnboardingChecklist component (was defined but never
  mounted).
- New useOnboardingStatus hook so page + components share one fetch contract.

Tests:
- Backend: test_onboarding_status_includes_email_verified_and_shop_setup_done.
- Frontend (Vitest): 13 new tests across NextStepCard, SetupChecklist, and
  QuickStartPage covering priority ordering, dismissal, the SOLO/TEAM
  removal, the toggle reveal, and the trial-stage gate on Pick a plan.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/api/onboarding.ts

@@ -4,11 +4,15 @@ export interface OnboardingStatus {
   created_flow: boolean
   ran_session: boolean
   exported_session: boolean
+  /** @deprecated Phase 2 — kept for backward-compat. New UI no longer branches on this. */
   tried_ai_assistant: boolean
   invited_teammate: boolean
   connected_psa: boolean
   is_team_user: boolean
   dismissed: boolean
+  // Phase 2 (Task 41) — drive the unified next-step card + checklist.
+  email_verified: boolean
+  shop_setup_done: boolean
 }
 
 export async function getOnboardingStatus(): Promise<OnboardingStatus> {