feat(examples): enable ValidationHookConfig at boot in v3 reference seller#400

bokelley wants to merge 3 commits intomainadcontextprotocol/adcp-client-python:mainfrom

claude/issue-387-v3-ref-seller-validation-hookadcontextprotocol/adcp-client-python:claude/issue-387-v3-ref-seller-validation-hookCopy head branch name to clipboard