fix: correct slugifyTitle hook example in documentation (#16306)

[Giorgiosaud]

What?

Fixed incorrect return statement in the slugifyTitle field hook example in the official documentation.

The example was generating a properly formatted slug but then incorrectly returning the original value instead of the slugified result.

Why?

This was a bug in the documentation that could mislead developers implementing automatic slug generation. The hook appeared to work, but in reality did nothing useful.

How?

• Changed return value to return slug in the example

Before/After

Before:

const slug = value.toLowerCase()... 
return value // ← bug

**Aftere:**
```ts
const slug = value.toLowerCase()... 
return slug

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