Add AG-UI Protocol Plugin for BotSharp#2

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Copilot wants to merge 8 commits intomasterfrom

copilot/fix-e1a8ade2-367e-4832-bb81-1faa18117cde

Commits on Oct 9, 2025

upate AgUiController
GreenShadeZhang
committed

Commits on Oct 10, 2025

fix ag-ui error
GreenShadeZhang
committed