Match the store-scraper-bot behaviour: DM the owner once per boot regardless of
commit, and report an unknown SHA rather than staying silent. Drop the store-
based dedup and the empty-SHA skip; resolveCommitSHA defaults to "unknown".
Baking SOURCE_COMMIT as a Docker build arg never worked: Coolify exposes it
as a runtime env var, not a build arg, so gitSHA was always empty and the owner
DM was skipped. Read SOURCE_COMMIT from the container env at startup (falling
back to the ldflags-baked gitSHA for local builds), forward it via the compose
environment, and drop the dead build-arg baking.
tiennm99