chore(dev): add contributor and agent workflow

[makors]

Adds an agent guide and a development helper for diagnosing Docker setup and running tests. Updates contributor documentation and adds helper tests to CI.

Validation: all 8 helper tests and full pre-commit checks pass. Live application tests were not run because Docker is stopped.

Generated by Codex.

[makors]

no idea if this is going to work

[coveralls]

coverage: 78.856% (-0.005%) from 78.861% — makors:chore/contributor-workflow into tjcsl:dev

[makors]

@greptileai review

[greptile-apps]

Confidence Score: 5/5

Safe to merge based on the exercised development-helper behavior and passing focused tests.

What we checked:

• Executed isolated CLI checks with mocked Docker responses for both checkout-mount outcomes.
• Observed that a Django container mounted from a different checkout exited with code 1 and did not invoke docker compose exec.
• Observed that a Django container mounted from the current checkout invoked manage.py test --noinput intranet.apps.polls -v 2 --keepdb and returned exit code 23.
• Ran the focused standard-library helper test suite; all eight tests passed.
• Compared behavior before and after capture; after capture the exact test command was invoked for the matching checkout and returned 23, while the docker daemon was available but no Compose services were running, implying the stack was driven by mocks.