removed wrong link for connectButton theme (#6937)

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## PR-Codex overview
This PR updates the link for the `ConnectButton` component's theme documentation from Notion to the official Thirdweb portal, ensuring users have access to the most accurate and current information.

### Detailed summary
- Changed the link for the `ConnectButton` component's theme documentation from Notion to the official Thirdweb portal.

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Author: GiselleNessi

apps/portal/src/app/connect/sign-in/customization/page.mdx

@@ -44,7 +44,7 @@ function Example() {
 
 ## Theming
 
-You can set the theme for the [ConnectButton](https://www.notion.so/ConnectButton-51113a400e614dfe93a598e9e1b8ef63?pvs=21) component, which is set to `"dark"` by default. theme can be set to either `"dark"` , `"light"` or a custom theme object.
+You can set the theme for the [ConnectButton](https://portal.thirdweb.com/references/typescript/v5/ConnectButtonProps#theme) component, which is set to `"dark"` by default. theme can be set to either `"dark"` , `"light"` or a custom theme object.
 
 We have **`[lightTheme](https://portal.thirdweb.com/references/typescript/v5/lightTheme)`** or **`[darkTheme](https://portal.thirdweb.com/references/typescript/v5/darkTheme)`** providers that you can override to kickstart customization.