[Bounty proposal] docs(cli): Japanese (ja) agent quickstart ($25 proposed)

Summary

sdks/python-cli/examples/agent_quickstart.md (the guide for Claude Code / Cursor / bot harnesses) is localized only to zh-CN and zh-TW. Propose adding a Japanese version, agent_quickstart.ja.md, following the exact structure of the accepted agent_quickstart.zh-CN.md.

Scope

• Add sdks/python-cli/examples/agent_quickstart.ja.md (7 H2 / 5 H3 / 11 code blocks, same as the English source)
• All shell commands and both Python blocks identical to the English source; only prose and inline comments translated
• Add the discovery line in sdks/python-cli/examples/README.md next to the zh-CN / zh-TW entries

Proposed bounty

$25 (same rate as the localized quickstart bounties). Native Japanese speaker; PR is ready to open. Related: #14572 (bringing quickstart.ja.md up to the current template).