[codex] Improve first viewport impression

[nopara73]

What changed

• Reworked the homepage first-viewport insert into a centered, lightweight lead-in instead of a stacked hero/dashboard surface.
• Kept the server-rendered leaderboard snapshot signal: athlete count, Pro/Amateur counts, the Ultimate League ordering rule, and the current Ultimate Buy SSL #1 link.
• Preserved the global PLAY THE GAME header CTA and removed the duplicate injected apply CTA, proof chips, dark stats panel, and duplicate athlete card.
• Let the existing podium remain the first strong athlete/photo moment, so the page reads as one coherent flow instead of competing modules.
• Made default config creation atomic to avoid parallel WebApplicationFactory startup races during tests.

Root cause

The previous no-scroll view did not explain the product clearly enough before the leaderboard finished bootstrapping. The first PR pass solved that with too much UI: duplicate CTAs, proof chips, a dark stats panel, and a second athlete card immediately above the real podium. This version keeps the useful server-rendered signal while letting the existing podium carry the emotional first impression.

Validation

• dotnet test LongevityWorldCup.Tests\LongevityWorldCup.Tests.csproj -v minimal passed: 111 tests.
• Ran a repo-local .NET Playwright smoke harness against 1440x900, 390x844, and 375x667.
• Verified no horizontal overflow, the first-viewport headline/status render, and the podium begins inside the first viewport on desktop, mobile, and short mobile.

Closes #538