[docs] Optimize large GIF assets used in Base Account guides

# [docs] Optimize large GIF assets used in Base Account guides

## Summary

Some docs pages embed relatively large GIF assets. Optimizing or replacing these with lighter formats could improve page load performance.

## Affected assets

- `docs/images/base-account/BasePayFinal.gif` — approximately 7.55 MB
- `docs/images/base-account/privy-base-auth.gif` — approximately 3.52 MB

## Usage

- `docs/base-account/guides/accept-payments.mdx`
- Line 62: `/images/base-account/BasePayFinal.gif`
- `docs/base-account/framework-integrations/privy/authentication.mdx`
- Line 25: `/images/base-account/privy-base-auth.gif`

## Expected improvement

Consider replacing large GIFs with optimized WebP/MP4 assets, reducing dimensions, or adding lighter previews where appropriate.

## How I found it

Scanned docs assets larger than 1 MB and checked where they are referenced.