docs: add image byte-budget tutorial

[MarshallBear1]

Summary

Adds one substantive written tutorial under a new Image Processing category. It demonstrates how to use React Native Skia's imperative API to resize and JPEG-encode a local image to a strict decoded-byte budget.

The linked tutorial includes:

• a standalone TypeScript implementation;
• exact Base64 decoded-byte accounting;
• dimension/quality search tradeoffs;
• explicit Skia object cleanup; and
• production caveats for alpha, EXIF orientation, memory, cancellation, and server-side validation.

The pattern is derived from production React Native work but the example is vendor-neutral, MIT-licensed, and has no application data or backend dependency.

Validation

• Link resolves publicly with HTTP 200.
• Example checked against @shopify/react-native-skia 2.6.2 with strict TypeScript settings.
• git diff --check passes.

[MarshallBear1]

Closing as a duplicate of #3985. Apologies for the duplicate submission.