`setActive({ beforeEmit })` changed to `setActive({ navigate })`

The beforeEmit callback in setActive() has been replaced with navigate. The callback signature has also changed:

await setActive({
  session: sessionId,
- beforeEmit: () => {
-   // Called before session is set
- }
+ navigate: ({ session }) => {
+   // Called with the session object
+   return '/dashboard';
+ }
});

The navigate callback receives an object with the session property and should return the URL to navigate to.