docs: fix AEP economics paper link

[tharune]

Summary

• Replace AEP-5's dead external economics paper URL with the local economics.pdf included beside the AEP
• Fix the publised typo in the same sentence

Verification

• Confirmed https://github.com/akash-network/AEP/blob/main/spec/aep-2/economics.pdf returns HTTP 404
• Confirmed src/content/aeps/aep-5/economics.pdf exists in this repository
• Ran git diff --check

[aktdenis]

hey, @tharune thanks so much for taking the time to catch these! always love when community members help us polish things up. just a quick heads up: these PRs actually landed in the wrong repo. could you close them here and recreate them over in AEPs repo?

https://github.com/akash-network/AEP

thanks again for the assist, appreciate it!

[tharune]

Thanks for the heads up. Closing this here and recreating it in the AEP repository as requested: akash-network/AEP#106