Inconsistency in frequency of Device "Last Seen" status updates

### Current Behavior

Original discussion here: https://github.com/FlowFuse/flowfuse/pull/3714#issuecomment-2060733844

### Expected Behavior

Polling status should not require an entire refresh of the full `device` object. We should either be using websockets, or have an endpoint that just allows us to get a status update for the device

### Steps To Reproduce

- Fire up a Device
- Go to the Device's "Overview" page and note that the "last seen" status is updated every 5 seconds
- Navigate to the "Snapshots" tab - note that the last seen status no longer updates.

### Environment

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

Compare the Device Overview and Snapshots pages to see how each currently obtains the “last seen” status, starting with the existing polling or refresh path. The issue is done when the status updates every 5 seconds on both tabs without refreshing the full device object, using an appropriate status endpoint or websocket.

Written by the indexing model from the issue text.