feat(setup): show running build version in the Setup tab bar

CI already computes <branch>-<short-sha> for image tags but never
surfaced it anywhere reachable from the app, so there was no way to
tell what's actually deployed on a booth without cross-referencing
komodo/resources.toml's TAG by hand.

Thread it through: CI passes BUILD_VERSION as a Docker build-arg,
the Dockerfile captures it as a runtime env var, GET /api/version
(gated by the existing site:read permission) exposes it, and the
Setup page's tab bar shows it right-aligned, muted, absent entirely
on a local/dev build with no CI-supplied value.

Claude-Session: https://claude.ai/code/session_01FWncR69HgGPuei1dLrW3cU

apps/server/Dockerfile

@@ -47,6 +47,11 @@ RUN --mount=type=cache,id=pnpm-store,target=/root/.local/share/pnpm/store \
 # ---- runtime: slim, non-root ----
 FROM node:22-alpine AS runtime
 WORKDIR /app
+# Set by CI to "<branch>-<short-sha>" (e.g. "stage-28bd838"), matching the same string used
+# as the Komodo Stack's TAG (komodo/resources.toml) — so the version shown in the app is the
+# same string an admin would look up there. Empty/absent on a local `docker build` (dev only).
+ARG BUILD_VERSION=""
+ENV BUILD_VERSION=$BUILD_VERSION
 ENV NODE_ENV=production
 RUN apk add --no-cache libstdc++   # better-sqlite3 native runtime
 RUN addgroup -S app && adduser -S -G app app