Move Sync connected sites to redux slice

[sejas]

Related issues

• Fixes STU-420

Proposed Changes

• Remove useSiteSyncManagement
• Implement connected sites as redux slice
• Update tests to use the Redux store
• No user-facing changes

Testing Instructions

• Run npm start.
• Go to the Sync tab.
• Connect a site.
• Observe that the site is connected.
• Restart the app.
• Observe that the connected site is still present.
• Connect another site.
• Observe that the newly connected site is unavailable.
• Try to disconnect the site.
• Observe that the site gets disconnected.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[ivan-ottinger]

The proposed changes look great! I did not observe any regressions when testing connecting and reconnecting sites. 👍🏼

Considering the size of the PR it would be great if one more person could review it.

[gcsecsey]

These changes look good to me too, and I also didn't encounter any regressions when testing. The connected sites are persisted between app restarts and I can connect multiple sites just as on the trunk version. 👍

Connecting a new site:

CleanShot.2025-09-02.at.14.56.21.mp4

After restarting the app, connecting and removing an additional site:

CleanShot.2025-09-02.at.15.05.15.mp4