MacOS: Multiple Instances & Virtual Machines on removable media

**Describe the issue**
When using it on a MacOS, with a Mac acting as a server.. rebooting results in a variety of complications, chief amongst them is:

- UTM does not refresh VM view .. when vm disk location not available at start(thus VM accessibility) for removable media located items, the application never refreshes its view or checks if accessible.

**Suggestion**: Can we make the UTM app periodically reload/retry for VM's which are marked as unavailable? it shows as greyed out, perhaps a setting on frequency as 0/dsiable or x seconds

> [!TIP]
> Workaround: Manually via cron start the application after a delay such that a sufficient amount of time has passed to allow the removable(plugged in) disk and mapped drives are loaded.

- UTM may be loaded on start up albeit not set up to start at start up. This is a problem if you have multiple instances and thus the command line scripting via utmctl targets the 1st launched instance. macOS is doing its thing when the application is brought to the foreground by some event or application-system crash.

Combined with above it makes for a fun why didnt it work, let me login and see what went down only to discover multiple instances and the primary initial instance has vms greyed out due to removable disk issue haha.

**Suggestion**: Could we have a setting to limit only one instance on the system?

> [!TIP]
> Workaround: More manual cron magic, i kill any instances post boot with delay so that when i relaunch there is there is only one instance.

**Configuration**
* UTM Version: 4.6.5
* macOS Version: 15.4.1
* Mac Chip (Intel, M1, ...): M1

So yah.. i worked around the issues but ideally these seem like features changes the application could make.