Well, you could use a
massive contactor, but I don't know if that would be acceptable per code for disconnecting a distribution panel (certainly you'd still need a more conventional disconnecting means upstream of it). Where are you located?
Union Connector do
remote controlled company switches*, but those are not really off-the-shelf items.
There are probably solutions in the backup power market, but I expect those would be more complicated since they would have to deal with interlocks to prevent crossfeeding and other loud and unpleasant mishaps. Also they're probably sold as packages to installers, so may be hard to buy a single standalone switch.
There are 'electrically operated circuit breakers' from the likes of
Eaton et al. Something like these may be what Union Connector use, I don't know, but they're really designed for big switchgear situations, not so much residential/light commercial setups.
If you have that much money tied up in the shed, you might be better off just insuring it against mishaps. Just make sure that there's absolutely nothing dodgy or homebrew-looking that the insurance company can use to get out from under a claim.
* Possibly not a common term outside the entertainment production industry, company switches are where you temporarily tie your equipment into building power, hundreds of amps at a time. They're found throughout arenas, convention centers, theaters, etc, and usually sport a set of 400A "camlock" connectors.