FlowFuse tries to start the same Node-RED instance more than once which results in a crash loop

### Current Behavior

```
18/02/2025 21:04:11 [system] Node-RED exited rc=1 signal=null
18/02/2025 21:04:11 [system] Node-RED unexpectedly stopped after: 9s
18/02/2025 21:04:11 [system] Starting Node-RED
18/02/2025 21:04:11 [system] Starting health check monitor (7.5s)
18/02/2025 21:04:13 [info] Welcome to Node-RED
===================

18/02/2025 21:04:13 [info] Node-RED version: v3.1.15
18/02/2025 21:04:13 [info] Node.js version: v18.20.5
18/02/2025 21:04:13 [info] Linux 5.10.230-223.885.amzn2.aarch64 arm64 LE
18/02/2025 21:04:14 [info] Loading palette nodes
18/02/2025 21:04:15 [info] FlowFuse Assistant Plugin loaded
18/02/2025 21:04:15 [info] FlowFuse HTTP Authentication Plugin loaded
18/02/2025 21:04:15 [info] FlowFuse Team Library Plugin loaded
18/02/2025 21:04:15 [info] FlowFuse Light Theme Plugin loaded
18/02/2025 21:04:15 [info] FlowFuse Dark Theme Plugin loaded
18/02/2025 21:04:15 [info] FlowFuse Metrics Plugin loaded
18/02/2025 21:04:19 [] spawnSync locale ENOENT
18/02/2025 21:04:20 [warn] ------------------------------------------------------
18/02/2025 21:04:20 [warn] [@flowfuse/nr-file-nodes/file] 'file in' already registered by module node-red
18/02/2025 21:04:20 [warn] ------------------------------------------------------
18/02/2025 21:04:20 [info] Settings file : /data/settings.js
18/02/2025 21:04:20 [info] Context store : 'memory' [module=memory]
18/02/2025 21:04:20 [info] Context store : 'persistent' [module=custom]
18/02/2025 21:04:20 [error] Unable to listen on http://127.0.0.1:1880/
18/02/2025 21:04:20 [error] Error: port in use
18/02/2025 21:04:20 [system] Node-RED exited rc=1 signal=null
18/02/2025 21:04:20 [system] Node-RED unexpectedly stopped after: 10s
18/02/2025 21:04:20 [system] Node-RED restart loop detected whilst in safe mode. Stopping.
18/02/2025 21:32:37 [info] Disconnected yX7adHFbYk3nAASyAAAB due to transport error
18/02/2025 21:33:01 [system] Stopping Node-RED
18/02/2025 21:33:11 [system] Node-RED stop timed-out. Sending SIGKILL
```

### Expected Behavior

No matter what a user clicks in the interface, they should not be able to get an instance into this state.

### Steps To Reproduce

We (actually @hardillb) speculated that this might be possible if the restart / start button is pressed at exactly the right time more than once.

That should not be possible.

### Environment

- FlowFuse version:
- Node.js version:
- npm version:
- Platform/OS:
- Browser:

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

I have provided an initial effort estimate

No source file or test is named. Start by tracing the interface handlers for the start and restart buttons and the Node-RED process lifecycle, then reproduce the problem with repeated clicks at startup. Done means user actions cannot launch duplicate instances or leave the instance in a port-conflict crash loop.

Written by the indexing model from the issue text.