Compare snapshot shows no differences

### Current Behavior

When doing a customer demo, I showed how we can compare snapshots. This did not work as expected.

NOTEs:
* No errors in console
* this snapshot reported "No differences" against all snapshots in the list
* the 2nd and following snapshots do have differences and the compare for those do work

### Expected Behavior

Should show changes from most recent snapshot to other snapshots

### Steps To Reproduce

* Visit https://app.flowfuse.com/instance/97650584-ccdf-47c3-8825-76893b653b4b/version-history/snapshots
* select snapshot `Auto Snapshot - 2025-09-03 09:48:19` for comparison
* select any other snapshot & click compare

### Environment

- FlowFuse version: FFC Live/current (2.21.0)
- Node.js version: NA
- npm version: NA
- Platform/OS: Win 11
- Browser: Chrome latest

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

I have provided an initial effort estimate