Remove SDK reference from kernel and add external package instead

[gentlementlegen]

          @whilefoo to fix that whole mess I ended up creating a separate repo for the SDK to avoid circular references and allow this to compile

https://github.com/ubiquity-os/plugin-sdk

I will update the kernel accordingly.

Running plugin as SDK: https://github.com/Meniole/text-conversation-rewards/actions/runs/11723241994/job/32654486608#step:3:17

Originally posted by @gentlementlegen in ubiquity-os-marketplace/text-conversation-rewards#170 (comment)

[ubiquity-os-beta]

@gentlementlegen the deadline is at Fri, Nov 8, 3:43 AM UTC

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