Wire up deployment metadata: build commit, number, and server start time; v2.0.30

- Dockerfile: expose BUILD_COMMIT and BUILD_NUMBER env vars from build args
  (was COMMIT_SHA only; server was reading BUILD_COMMIT so it always fell through to null)
- CI: pass github.run_number as BUILD_NUMBER build arg
- state.js: record serverStartedAt at module load so deployedAt always shows
  when the current container instance came up, even without an env var
- admin-content.js: fall back COMMIT_SHA → BUILD_COMMIT for older images,
  use state.serverStartedAt when DEPLOYED_AT env var not set

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

Dockerfile

@@ -12,7 +12,9 @@ ENV NODE_ENV=production
 ENV PORT=4173
 
 ARG COMMIT_SHA=unknown
-ENV COMMIT_SHA=${COMMIT_SHA}
+ARG BUILD_NUMBER=unknown
+ENV BUILD_COMMIT=${COMMIT_SHA}
+ENV BUILD_NUMBER=${BUILD_NUMBER}
 
 COPY --from=deps /app/node_modules ./node_modules