Fixes#192 — script and GHCR update flows now drop data/.last_update_result.json
the same way betterdesk.sh already does, so a failed in-panel attempt no longer
sticks around after a successful external update.
The panel updater assumed a native install with Go source on disk. In
Compose/GHCR mode it now uses the embedded image commit, clears stale
binary markers, and directs operators to pull new container images instead.