Add build scripts, fix GCC warnings, unify CI workflows

- Add scripts/clean.sh, test.sh, build.sh, lint.sh as single source
  of truth for local and CI builds (always clean, always parallel)
- Fix -Wmissing-braces: replace {{0}} with memset for struct arrays
- Fix -Wrestrict: use intermediate buffer for same-struct snprintf
- Update dry-run.yml and release.yml to use the new scripts