fix(docs): Rename spacerace to referrals for nav item (#4477)

# Description of Changes
- Rename `Spacerace` to `Referrals` for docs nav item to align with
updated naming

<!-- Please describe your change, mention any related tickets, and so on
here. -->

# Screenshots
- After:
<img width="1510" height="49" alt="image"
src="https://github.com/user-attachments/assets/3bdbe6ec-8a51-4686-9292-28c38b6d14d9"
/>

- Before:
<img width="1460" height="47" alt="image"
src="https://github.com/user-attachments/assets/5c70b0ef-d5fc-42fa-9dc9-5fd4f034d415"
/>


# API and ABI breaking changes

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corresponding GitHub label. -->

# Expected complexity level and risk
1

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# Testing

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reviewers to do,
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- [x] Docs displays correctly

Author: clockwork-tien

docs/docusaurus.config.ts

@@ -186,7 +186,7 @@ const config: Config = {
         },
         {
           href: 'https://spacetimedb.com/space-race',
-          label: 'Spacerace',
+          label: 'Referrals',
           position: 'right',
         },
         {