fix: ui and ui-dev containers conflict on port 4000

[mihow]

Problem

Running docker compose --profile ui-dev up also starts the default ui container, since it has no profiles: key. Both bind port 4000, causing a conflict. Developers must manually docker compose stop ui before starting ui-dev.

Options

A. Add a profile to the ui service

Put ui under profiles: [default, ui] and ui-dev stays under profiles: [ui-dev]. Then:

• docker compose --profile default up (or a wrapper script) starts the production-like UI
• docker compose --profile ui-dev up starts the hot-reload UI
• Plain docker compose up starts neither — this is the breaking change

Pro: Clean separation, no port conflict possible.
Con: Changes the default developer experience — everyone must pass --profile default (or --profile ui) to get a UI.

B. Use different ports

Change ui-dev to bind a different host port (e.g., 4001:4000). Both can run simultaneously.

Pro: No workflow change, backwards compatible.
Con: Developers need to know which port to use. Having both running wastes resources.

C. Use COMPOSE_PROFILES env var

Document setting COMPOSE_PROFILES=ui-dev in .env or shell profile to opt into dev mode. Keep ui as-is (no profile). Add profiles: [ui] to ui so it only starts when explicitly requested or when no profile is set... but Compose doesn't work that way.

This doesn't actually solve the conflict without also applying option A.

D. Override file approach

Move ui-dev into docker-compose.override.yml (git-ignored) that replaces the ui service with the dev variant. Developers copy a template file.

Pro: No profile juggling, docker compose up just works with the right UI.
Con: Another override file to manage. We already use this pattern for debugpy.

Recommendation

Option A is the cleanest long-term, but needs a CLAUDE.md / README update. Option D fits the existing override pattern we use for debugpy.