v0.42.56.2 fix(ci): frozen-lockfile + fail-fast:false + test timeout …

…in Release workflow

fix(docker): add setup-buildx-action for gha cache backend

gha cache requires the docker-container driver; the default docker driver
does not support cache export.

Co-Authored-By: Claude <noreply@anthropic.com>

feat(docker): add Dockerfile, .dockerignore, and GHCR publish workflow

Co-Authored-By: Claude <noreply@anthropic.com>

v0.35.1.0 baseline for the OpenAI vs Voyage vs ZE embedder shootout (…

…see docs/designs/2026_05_EVAL_PLAN.md, PR garrytan#1055)