Update favicon to Dev Proxy icon (#33)

* Initial plan

* Update favicon with Dev Proxy icon from dotnet/dev-proxy repo

Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

Author: Copilot