ac-os: parallel binary build + consistent version strings
- Add -j$(nproc) to binary make (was single-threaded on 8 cores)
- Freeze AC_GIT_HASH, AC_BUILD_TS, AC_BUILD_NAME once at script top
- All stages (build, initramfs, kernel, upload, record) use the same
frozen values — no more mismatches from HEAD moving mid-build
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>