Add Portfolio Pro $99/mo checkout on pricing page

[Alexaliao001]

Summary

Adds Portfolio Pro ($99/mo, monthly only) as a buyable third tier on /pricing, wired to Stripe livemode product quantradar_portfolio_pro_monthly_v1.

What changed

• Pricing page — three cash registers: Free, Pro ($29/mo + yearly toggle), Portfolio Pro ($99/mo, monthly only)
• Checkout — POST /api/billing/checkout accepts { "plan": "portfolio_pro" } and resolves price from STRIPE_PRICE_ID_PORTFOLIO_PRO_MONTHLY
• Webhook — checkout.session.completed with metadata.product=quantradar_portfolio_pro sets plan=portfolio_pro
• Access — portfolio_pro gets the same paid desk privileges as Pro (live gate, public surface)
• Copy — honest: same desk access as Pro on this host today; portfolio batch/report workflow is roadmap, not sold as live

Deploy prerequisite (Render env)

Set on quantradar-shell:

STRIPE_PRICE_ID_PORTFOLIO_PRO_MONTHLY=price_1TDM067uBhbslGrGtxzYXEq1

Existing Pro vars unchanged (STRIPE_PRICE_ID_MONTHLY=price_1TDM027uBhbslGrGK7mMVtEp).

How to verify in livemode

1. Deploy with STRIPE_PRICE_ID_PORTFOLIO_PRO_MONTHLY set to the live price above
2. Sign in at https://quantradar.one/pricing
3. Click Get Portfolio Pro → should redirect to Stripe Checkout for $99/mo
4. Complete test payment → webhook should set plan=portfolio_pro in user store
5. Confirm /api/auth/status returns "plan": "portfolio_pro"

Tests

All 88 unit tests pass, including new portfolio checkout metadata and webhook tests.