Update Brand Kit link in footer to point to base.org/brand

[juandolealt]

What changed? Why?

This PR updates the Brand Kit link in the footer from https://github.com/base/brand-kit to https://www.base.org/brand to point to the new brand guidelines page.

Notes to reviewers

How has it been tested?

Locally

Have you tested the following pages?

BaseWeb

• [] base.org
• [] base.org/names
• [] base.org/builders
• [] base.org/ecosystem
• [] base.org/name/jesse
• [] base.org/manage-names
• [] base.org/resources

[vercel]

@juandolealt is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[cb-heimdall]

🟡 Heimdall Review Status

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Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2