[pixels-CI] Unify GitHub Actions secret naming and replace softprops/action-gh-release with native gh CLI

[AntiO2]

Background

The daily-build.yml workflow currently uses the third-party softprops/action-gh-release@v2 action to manage daily releases, and the secret parameter name passed between daily-build.yml and
remove-daily-latest.yml is inconsistent (gh_token vs PIXELS_DEVELOP).

Changes

1. Unify secret parameter name to PIXELS_DEVELOP across both workflows
2. Replace softprops/action-gh-release@v2 with native gh release create/edit/upload commands
3. Add explicit permissions: contents: write, actions: write to daily-build.yml
4. Add .github/workflows/README.md with setup guide for PIXELS_DEVELOP secret, token creation, and troubleshooting