Update overview.mdx (#1507)

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> [!IMPORTANT]
> Update `baml_client` card link in `overview.mdx` to point to
`/ref/baml-client/type-builder`.
> 
>   - **Navigation Update**:
> - Update `href` for `baml_client` card in `overview.mdx` from
`/ref/baml-client` to `/ref/baml-client/type-builder`.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for d2e35a3. It will automatically
update as commits are pushed.</sup>

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fern/03-reference/overview.mdx

@@ -29,7 +29,7 @@ For more in-depth explanations, we recommend reading the [Guides](/guide) first.
     LLM clients and how to configure them.
   </Card>
 
-  <Card title="baml_client" icon="fa-solid fa-running" href="/ref/baml-client">
+  <Card title="baml_client" icon="fa-solid fa-running" href="/ref/baml-client/type-builder">
     API Reference for the `baml_client` object.
   </Card>