footer: unify the receipt + identity into one terminal session panel; fix HEAD sha in container builds (GIT_SHA build-arg)

Dockerfile

@@ -13,7 +13,10 @@ WORKDIR /app
 COPY package.json package-lock.json ./
 RUN npm ci
 
-# Build the static site.
+# Build the static site. The git sha arrives as a build-arg (.dockerignore excludes .git,
+# so an in-container `git rev-parse` can never resolve — the footer receipt read "HEAD unknown").
+ARG GIT_SHA
+ENV GIT_SHA=${GIT_SHA}
 COPY . .
 RUN npm run build