Show Chinese and English in the root README

[ParuhParhat]

Summary

• render Chinese and English together in the root README.md so the repository homepage is visibly bilingual
• use bilingual titles, introductions, feature descriptions, architecture notes, build instructions, limitations, and license guidance
• add the published v1.0.0 APK download and release links near the top
• remove the now-redundant standalone README_EN.md

User impact

Visitors can read both languages directly on the repository homepage without opening a separate file.

Validation

• verified every local README link resolves
• verified there are no remaining README_EN.md references
• ran git diff --check and git diff --cached --check
• GitHub Actions CI validates the updated PR