Add the optional, backward-compatible SOURCE_IMAGE branch to
orchestrator-deploy-hook.sh: when set, retag the staging-validated image
onto TARGET_IMAGE (docker tag) before `up -d --no-build` instead of
rebuilding — guarantees prod runs the exact artefact that passed staging
(AC-7 / TC-14). Unset -> prior behaviour; exit-code contract (0/1/2) and
health-loop untouched.
Update golden-source docs (AC-13): rewrite deployer.md `deploy` stage from
"paper SUCCESS" to the executable self-deploy (Phase A/B/C, no self-restart
from inside the container) and add the ORCH-036 CHANGELOG entry.
Refs: ORCH-036
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
