fix: resolve Docker container startup error with entrypoint script

- Created docker-entrypoint.sh script to properly start Next.js server
- Script explicitly changes to /app directory and runs node server.js
- Updated Dockerfile to copy and use the entrypoint script
- This fixes the "Cannot find module '/server.js'" error
- Makes deployment more robust against container orchestration overrides

The container now has a proper entrypoint that Portainer expects
and correctly starts the Next.js standalone server.

🤖 Generated with Claude Code

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

docker-entrypoint.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -e
+
+# Change to app directory
+cd /app
+
+# Start the Next.js server
+echo "Starting Next.js server..."
+exec node server.js