feat(web): redesign login page and proxy strategy market to vergex.trade

- LoginPage: two-column desktop layout with brand panel (status pill,
  gradient headline, stats strip) and form panel; single-column mobile
  layout with centered brand mark. Self-contained grid centering so
  layout no longer depends on parent flex behavior. Drop the dead
  OnboardingModeSelector (it belongs to SetupPage, not login) and add
  loader spinner, animated submit arrow, and clearer error banner.
- StrategyMarketPage: replace the 560-line bespoke marketplace with a
  branded handoff to vergex.trade/explore. Direct iframe embedding is
  currently blocked by vergex's X-Frame-Options: SAMEORIGIN and
  frame-ancestors 'self', and there is no way to reliably detect the
  block from JavaScript (load event fires for the browser error page,
  contentWindow.location throws SecurityError in both success and
  failure). The component now renders a centered card with the
  POWERED BY VERGEX.TRADE pill, headline, description, gold CTA, and
  a stats row, with all three supported languages.
- .gitignore: exclude .gstack/ (local security audit reports).

.gitignore

@@ -133,3 +133,4 @@ PR_DESCRIPTION.md
 
 # Go build artifacts
 /nofx-server
+.gstack/