Reorder sponsor tiers: Susquehanna to diamond, ContestDojo to gold

[devin-ai-integration]

Summary

Moves Susquehanna from the Gold Sponsors tier to Diamond, and ContestDojo from Diamond to Gold, for better visual balance on the homepage sponsor listing.

• Diamond (4 sponsors): Citadel, Susquehanna, Jane Street, blackpenredpen
• Gold (2 sponsors): Atomic Grader, ContestDojo

Also adds per-sponsor img_class override support in the template (sponsor.img_class | default(value=tier.img_class)), used here to give Susquehanna a wider constraint (max-w-48) since its logo has a high aspect ratio and appeared too small at the default diamond tier max-w-36.

Updates since last revision

• Swapped Susquehanna and Jane Street order within Diamond tier (Susquehanna now appears second, after Citadel)

Review & Testing Checklist for Human

• Verify the sponsor.img_class | default(value=tier.img_class) Tera filter works correctly in production — confirm sponsors without a custom img_class still get the tier default and don't error
• Check that Susquehanna at max-w-48 looks appropriately sized relative to other diamond sponsors on both desktop and mobile viewports
• Verify ContestDojo logo renders correctly at gold tier sizing (max-w-64 max-h-12) — it was previously at diamond sizing
• Confirm the 4-sponsor diamond row doesn't wrap awkwardly on narrower screens

Suggested test plan: Deploy the preview and check the homepage sponsor section at desktop, tablet, and mobile widths. Verify all sponsor logos render and link correctly.

Notes

• Link to Devin run
• Requested by @oliver-ni

[devin-ai-integration]

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