Fix add to cursor button links (#6801)

It seems they are using [their own protocol/deeplink
scheme](https://docs.cursor.com/en/tools/developers#mcp-servers) now.

Fixes #6797

**Staged:**
https://dart-dev--pr6801-fix-6797-1g3x1h47.web.app/tools/mcp-server#cursor

Author: parlough

src/content/tools/mcp-server.md

@@ -200,8 +200,8 @@ documentation for [enabling MCP support][].
 The easiest way to configure the Dart and Flutter MCP server with
 Cursor is by clicking the **Add to Cursor** button:
 
-[![Add to Cursor](https://cursor.com/deeplink/mcp-install-dark.svg)](https://cursor.com/install-mcp?name=dart&config=eyJ0eXBlIjoic3RkaW8iLCJjb21tYW5kIjoiZGFydCBtY3Atc2VydmVyIC0tZXhwZXJpbWVudGFsLW1jcC1zZXJ2ZXIgLS1mb3JjZS1yb290cy1mYWxsYmFjayJ9){:.light-mode-visible}
-[![Add to Cursor](https://cursor.com/deeplink/mcp-install-light.svg)](https://cursor.com/install-mcp?name=dart&config=eyJ0eXBlIjoic3RkaW8iLCJjb21tYW5kIjoiZGFydCBtY3Atc2VydmVyIC0tZXhwZXJpbWVudGFsLW1jcC1zZXJ2ZXIgLS1mb3JjZS1yb290cy1mYWxsYmFjayJ9){:.dark-mode-visible}
+[![Add to Cursor](https://cursor.com/deeplink/mcp-install-dark.svg)](cursor://anysphere.cursor-deeplink/mcp/install?name=dart&config=eyJ0eXBlIjoic3RkaW8iLCJjb21tYW5kIjoiZGFydCBtY3Atc2VydmVyIC0tZXhwZXJpbWVudGFsLW1jcC1zZXJ2ZXIgLS1mb3JjZS1yb290cy1mYWxsYmFjayJ9){:.light-mode-visible}
+[![Add to Cursor](https://cursor.com/deeplink/mcp-install-light.svg)](cursor://anysphere.cursor-deeplink/mcp/install?name=dart&config=eyJ0eXBlIjoic3RkaW8iLCJjb21tYW5kIjoiZGFydCBtY3Atc2VydmVyIC0tZXhwZXJpbWVudGFsLW1jcC1zZXJ2ZXIgLS1mb3JjZS1yb290cy1mYWxsYmFjayJ9){:.dark-mode-visible}
 
 Alternatively, you can configure the server manually: