feat(examples): add 4 spec-required sales-* methods to v3 reference seller#394

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

claude/issue-376-v3-ref-seller-sales-methodsadcontextprotocol/adcp-client-python:claude/issue-376-v3-ref-seller-sales-methodsCopy head branch name to clipboard