Prepare beta release and project discovery

[xiaohei210509]

What changed

• adds a downloadable universal macOS beta release path with SHA-256 checksums
• adds English and Simplified Chinese UI localization
• rewrites the repository landing page in English and adds a Chinese README
• adds a real app screenshot and GitHub social preview asset
• adds privacy, security, troubleshooting, contribution, conduct, issue, and PR guidance
• makes CI build and verify the same universal ZIP users will download
• adds a tag-triggered GitHub Release workflow

Why

The repository previously required every user to install Xcode and build from source. That made community promotion likely to generate views but very few successful installs. These changes create a transparent community beta that users can download, verify, and run while clearly disclosing the current ad-hoc signing and notarization limitation.

Verification

• 8 XCTest cases pass
• English and Simplified Chinese localization selection is covered by tests
• universal release package contains both arm64 and x86_64
• final extracted ZIP passes strict code-sign verification
• Info.plist version/build metadata and both localization resources are verified
• SHA-256 checksum validation passes
• app launches from the extracted release bundle
• secret and machine-path scan found no credentials or /Users/zxh paths