Multi-stage backend/Dockerfile (sdk build -> aspnet:10.0 runtime, ~312MB) +
docker-compose.prod.yml, additive only — not wired into CI or the existing
dev docker-compose.yml (which keeps the SDK image for dotnet run hot-reload).
New .dockerignore keeps the build context lean (node_modules alone is
~750MB) since the Dockerfile COPYs from the repo root to pick up
public/letter.css (WP-25's FE<->BE letter contract) as a sibling of backend/.
Verified for real: built the image, ran it, and curled a live
GET /api/v1/brief/preview against the running container — got back the
actual rendered letter HTML with letter.css inlined, confirming the
walk-up-from-BaseDirectory lookup resolves inside this image layout too.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
