[7827] Improve UI for device status

[n-lark]

Description

Routes the new computed device status to onlineStatus (online/offline/never-seen). Collapses the device tables' "Last Seen" + "Last Known Status" columns into a single "Status" pill with last-seen and last-reported state in a tooltip.

Items to note

• I left the top "Last Seen" + "Last Known Status" grid things alone, lmk if we want any changes for those.
• The device detail page now feels a little inconsistent with the list view. I didn't make any changes but I can make a follow up if we'd like. Lmk!

Related Issue(s)

Resolves #7827

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label