docs(readme): improve README guide

[XiaoFeiASK]

Summary

Supplement README_CN.md and README_JP.md with documentation content that already exists in the latest English README.md.

This PR fills missing localized sections in the Chinese and Japanese README files by translating/localizing the corresponding English README content. It preserves the original product meaning, setup semantics, and wording style of each language version.

Changes

• Supplement the Why PowerMem section in the Chinese and Japanese README files based on the English README
• Add the existing AgentScope entry from the English SDKs & apps integration table to the Chinese and Japanese README files
• Supplement the standalone AgentScope integration section in Chinese and Japanese
• Supplement the existing uvx powermem-mcp wrapper usage for zero-install MCP clients in Chinese and Japanese
• Supplement the existing refresh/upgrade instruction for cached uv tool environments in Chinese and Japanese
• Align the Chinese integration section title with the English README for consistency

Notes

• The added sections are translated/localized from the existing English README content.
• This PR only supplements missing localized documentation and does not introduce new documentation semantics.
• No product behavior or code changes are included.
• Benchmark numbers, release highlights, and setup semantics are unchanged.
• The update only closes content gaps between the localized README files and the English README.

Verification

• Ran git diff --check -- README_CN.md README_JP.md
• Confirmed no whitespace errors
  related: docs(readme): improve README guide #1199

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