Fix version commit SHA showing as unknown in Docker (v1.0.1)

The runtime image doesn't include .git, so git rev-parse failed at
startup. Fix: pass COMMIT_SHA as a Docker build arg from github.sha
in CI and bake it into the image as an ENV var, which config.js
already prefers over running git.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -13,6 +13,9 @@ WORKDIR /app
 ENV NODE_ENV=production
 ENV PORT=4173
 
+ARG COMMIT_SHA=unknown
+ENV COMMIT_SHA=${COMMIT_SHA}
+
 COPY package*.json ./
 RUN npm ci --omit=dev --legacy-peer-deps