modify dockerfile.dev and compose.yaml

[mjacquot1]

What github.com/wevote/WebApp/issues does this fix?

Epic: https://wevoteusa.atlassian.net/browse/WV-4285
Child: https://wevoteusa.atlassian.net/browse/WV-4286

Changes included this pull request?

• Run containers as a non-root user. This reduces the potential impact of any malicious scripts by limiting system-level access.
• Use a named volume for node_modules. This prevents leftover or “dangling” dependencies from persisting across builds and causing inconsistencies. (Addendum, anonymous volumes persist after docker compose down, and on relaunching the container a new volume is created. This leaves a dangling volume of ~750mb)
• Adopt multi-stage Docker builds. Dependencies will be installed during the image build process rather than at runtime, ensuring a more controlled and reproducible environment.