docs: add Simplified Chinese and Japanese READMEs

[tura-ai-agent]

Adds complete Simplified Chinese and Japanese translations of the README and links them from the English README.

The translations preserve links, images, tables, and command examples.

[Julian-adv]

Thanks for the translations — merged! The quality was good overall: links, images, tables, and command examples all carried over correctly.

I fixed a few issues in a follow-up commit (ed626a7):

• Agent Client tech stack: both translations listed "MCP server (rmcp)" and dropped "Axum (local spectator panel)". rmcp is not part of master's agent-client (it only exists on an unmerged branch), so I restored the list to match the English README.
• Restored the tools/systemd/ reference in the Production Deployment section, which was dropped in both translations.
• ja: changed the "pants" equip slot from 「脚」 to 「ズボン」.

For future translation PRs, please translate from the current master state of README.md rather than any in-progress branches.