Migrate all image src references in README.md and README_CN.md from
./docs/generated/ and ./docs/screenshots/ to ./assets/generated/ and
./assets/screenshots/ to match the actual directory structure.
Also replace an external GitHub user-attachments URL with a local
./assets/screenshots/frontend-ui.png path in README.md.
- Add Apache 2.0 license badge to both README.md and README_CN.md
- Add Python 3.12+ version badge with logo
- Add Gitee Sync workflow status badge linking to GitHub Actions
- Improve project visibility with standardized badge indicators
- Replace BROKER_URL and RESULT_BACKEND with REDIS_DB_CELERY_BROKER and REDIS_DB_CELERY_BACKEND in README.md
- Replace BROKER_URL and RESULT_BACKEND with REDIS_DB_CELERY_BROKER and REDIS_DB_CELERY_BACKEND in README_CN.md
- Update api/env.example with new variable names and add deprecation notice
- Add reference to celery-env-bug-report.md documentation explaining why old variable names are avoided
- Prevents environment variable hijacking by Celery CLI when using standard naming conventions