fix: add rm -rf .next before build in Dockerfile (stale Turbopack cache)

The production Docker build was caching old .next chunks. Adding 'rm -rf .next'
before 'npm run build' ensures a fresh build every time, picking up code changes.

Dockerfile

@@ -17,6 +17,8 @@ ENV NEXT_TELEMETRY_DISABLED=1
 ENV DATABASE_URL="file:/app/db/custom.db"
 RUN apt-get update && apt-get install -y --no-install-recommends openssl && rm -rf /var/lib/apt/lists/*
 RUN npx prisma generate
+# Clean any stale .next cache before building
+RUN rm -rf .next
 RUN npm run build
 
 # --- Stage 3: Runner ---