Convert splash background image from png --> compressed jpg

[spwoodcock]

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation
• 🧑‍💻 Refactor
• ✅ Test
• 🤖 Build or CI
• ❓ Other (please specify)

Describe this PR

• The background image of the home/splash page is far too big - 1MB+
• It's also a .png instead of .jpg.
• The page rendering time is greatly reduced having to load this large payload.
• JPEG compression is much more efficient for lossy images such as this, reducing the image size by 10x --> ~70KB.

Screenshots

Compressed and zoomed it it still looks fine as a background:

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• 📗 Update any related documentation and include any relevant screenshots.

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