fix: prevent phantom badges in bridged rooms

[andrewmurphyio]

Fixes #2589

Fixes phantom unread badges appearing in bridged rooms (e.g., Slack, Discord bridges) where read receipts do not sync back to Matrix.

Problem

When using bridged rooms, reading messages on the other side (e.g., in Slack) does not update the Matrix read receipt. This causes roomHaveUnread() to return true even when the server notification count is 0, resulting in phantom badges.

Solution

Make the server notification count authoritative. Only add a room to the unread list if the server actually reports notifications (total > 0 or highlight > 0). This prevents phantom badges while still respecting the server's notification state.

Testing

1. Set up a bridged room (e.g., Slack bridge)
2. Read messages on the bridge side (not in Cinny)
3. Refresh Cinny
4. Previously: phantom badge would appear
5. Now: no badge if server reports 0 notifications

[vrisalab]

I've been testing this for a week, and it fixes the issue on a single client. Sadly, when using multiple devices (Desktop and a phone for example), ghost notifications for things read on one device appear on the other device. I'm not sure if this is easily fixable, though.