Add notifications tab and system delivery

[asyncFlow-dad]

Summary

• add a notifications tab in the notch UI and hook it to the coordinator
• introduce NotificationCenterManager and NotchNotification model for in-app + macOS banner delivery with retention
• expose notification settings (categories, delivery style, sound, DND, history) and document the feature

Testing

• Not tested (manual verification needed)

[Alexander5015]

I updated the tbase branch to dev, could you update the branch to exclude the commits made to main, just to keep the git history cleaner?