fix: improve checks for moving shares/storages into other mounts

[icewind1991]

• Also check for any mounts inside moved folders
• Throw an exception with a meaningful message instead of returning false
• have the webui show the message instead of a generic error

Fixes #44249

[icewind1991]

/compile /

[icewind1991]

I'll rebase + recompile when approved cause the js files are going to keep conflicting

[icewind1991]

/compile /

[icewind1991]

Annoyingly transfer ownership relies on the broken behavior of silently not moving mounts inside folders.

Added an option to ignore nested mounts when renaming folders. I hate it but doing it "properly" would be a pain.