fix(mpc-service): use docker-entrypoint.sh instead of inline script

- Restore Dockerfile to use external docker-entrypoint.sh file
- The inline echo script caused issues on Linux (start.sh not created properly)
- Change from prisma migrate deploy to prisma db push for schema flexibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/mpc-service/docker-entrypoint.sh

@@ -4,8 +4,8 @@ set -e
 echo "=== MPC Service Starting ==="
 echo "Running database migrations..."
 
-# Run migrations (standard production approach - fail if migration fails)
-npx prisma migrate deploy
+# Sync database schema (use db push for flexibility with schema changes)
+npx prisma db push --skip-generate
 
 echo "Database migrations completed"
 echo "Starting application..."