Add verification steps to check pre-built files exist

This will fail fast if LFS files weren't pulled properly.

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

Dockerfile

@@ -3,7 +3,7 @@ FROM node:20-slim
 # Set noninteractive installation
 ENV DEBIAN_FRONTEND=noninteractive
 
-# Build timestamp to force cache invalidation: 2026-01-12T20:50
+# Build timestamp to force cache invalidation: 2026-01-12T21:00
 
 # Install build dependencies
 RUN apt-get update && apt-get install -y \
@@ -33,6 +33,10 @@ RUN npm install --omit=dev && \
 # - Backend: backend/dist/backend/src/server.js
 # - Parser: public/lib/tgnParser.cjs
 
+# Verify dist files exist (will fail if LFS files weren't pulled)
+RUN test -f app/dist/index.html || (echo "ERROR: app/dist/index.html not found" && exit 1)
+RUN test -f backend/dist/backend/src/server.js || (echo "ERROR: backend/dist/backend/src/server.js not found" && exit 1)
+
 # Set environment variables for Hugging Face Spaces
 ENV PORT=7860
 ENV HOST=0.0.0.0