Release v0.1.0-beta.3

[Reyppp]

Summary

• publish the performance, progress, cache, single-instance, and native Explorer folder-selection updates as v0.1.0-beta.3
• update README and GitHub Pages with direct installer, SHA-256, release-note, installation, upgrade, and SmartScreen guidance
• keep the release marked as an unsigned Windows x64 beta and document the known single-layer detail display issue

Validation

• 23/23 unit tests passed with the Y226080 golden sample; test_golden_run was not skipped
• index.html JavaScript passed node --check
• website checked at 1440, 1280, 900, and 390 px without horizontal overflow
• sensitive-content scan found no real furnace data, local paths, settings, runtime tokens, certificates, installers, or context-summary.md in the commit

Release gate

Keep this PR and the tag-created release in draft until Windows CI/build, CI-produced SHA-256 verification, packaged smoke test, install/uninstall, and native folder-picker acceptance all pass.