Thanks @Henkka22, that got the distro repo links working again for me!
To get the Hak5 repo working again requires a little fussing... the OpenWRT wget on Shark Jack doesn't support TLS. Once you've got the basic distro repos working again (and can opkg update them), you need to also run the following commands:
opkg install ca-bundle
opkg install ca-certificates
opkg install libustream-mbedtls
This let me get the Hak5 repo working again too. (I spent waaaaaay too long diagnosign why wolfssl didn't work before uninstalling it and going with mbedtls.)