release.sh writes updates/manifest.json at release time (predictable
asset URL) — no CI commit-back, no push-token problem, no detached
checkout dance. release_publish.sh is create-release + upload only.
Manifest sha256 now optional; updater skips verification with a note
when absent (HTTPS + gzip CRC cover the realistic cases). Fixed the
repo-URL sed keeping a .git suffix (caught by a worktree dry run).
Updater tests: 8 (sha-less manifest flow added).