test infra: docker compose files referenced in tests are missing from repo

[agents-squads]

Problem

The infra tests reference a docker/ directory (containing a docker-compose file) that does not exist in the repository. Any contributor or user who attempts to reproduce or run infra tests locally hits an immediate dead end — there is nothing to infer from, and no way to know what the missing folder should contain.

This was reported in #594 by an external contributor who investigated thoroughly and correctly identified this as a repo-side gap, not a user error.

Impact

• External contributors cannot reproduce or run infra tests
• The gap is invisible until someone specifically tries to contribute — at which point there is no path forward without internal knowledge
• We incorrectly asked the reporter to contribute a fix when only the team can know what belongs in the missing folder

Steps to Reproduce

1. Clone the repo
2. Run the infra tests (or search for docker compose references in src/ or tests/)
3. Observe references to a docker/ path that does not exist

Acceptance Criteria

• Identify all code/script references to the missing docker/ path
• Either: add a working docker-compose setup to the repo, or remove the broken references if the folder is no longer needed
• Infra tests are reproducible by an external contributor with no internal knowledge
• CONTRIBUTING.md accurately reflects how to run tests locally

Related

Closes #594 (external contributor hit this blocker — loop is now closed with them)