fix(e2e): rewrite card and crypto payment flow specs

Rewrite both payment specs to match current BillingPanel UI:
- Use correct API endpoints (/payments/stripe/purchasePlan, /payments/stripe/currentPlan)
- Don't assert specific plan tier in purchase body (Upgrade may hit BASIC or PRO)
- Handle crypto toggle limitation on Mac2 (accessibility clicks don't reliably update React state)
- Verify billing page loads and plan data is fetched after payment

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: CodeGhost21