Feat/containerized dev stack

[JoelLarson]

Summary

This PR cleans up the dev startup flow so local runs no longer try to manage Valkey manually, and containerized runs remain explicitly supported via CONTAINERIZED=1.

What changed

• Local make up now delegates to bin/dev
• bin/dev checks that Valkey is already listening on the configured Redis port before starting Rails
• If Valkey is not reachable, startup fails fast with a clear warning
• make up CONTAINERIZED=1 still uses the Docker Compose path
• README updated with clearer local vs containerized run instructions

Why

The old setup assumed systemctl was available and able to start Valkey, which does not work on macOS and is not the right responsibility for the app startup path. This change makes local dev behavior explicit and cross-platform, while keeping the containerized override intact.

Verification

• Confirmed make up resolves to bin/dev in the local path
• Confirmed make up CONTAINERIZED=1 resolves to docker compose up --build
• Checked the branch diff against origin/main to ensure the containerized override still works