docs: rewrite open-source readmes

[Pigbibi]

Summary

• rewrite the repository README as an open-source project entry point rather than an internal build log
• keep README.md English-only and README.zh-CN.md Chinese-only
• document where the repository sits in the QuantStrategyLab architecture, including strategy package, snapshot pipeline, platform runtime, shared infrastructure, or research/audit boundaries
• split direct runtime strategies from snapshot-backed strategy evidence where applicable

Validation

• verified README.md contains no Chinese characters
• verified README.zh-CN.md exists and contains the Chinese risk notice
• verified required architecture sections are present
• verified only README.md and README.zh-CN.md changed

Notes

• HK strategy repositories are intentionally excluded from this batch because their profile names are being changed in another workstream.