chore: add make lint/test entrypoints and fix repo URLs in CONTRIBUTING

[michaelxu2288]

What

• CONTRIBUTING.md pointed at scaleapi/agentex.git / cd agentex; the repo is scale-agentex.
• CONTRIBUTING tells contributors to run make test and make lint from the repo root; neither target existed at the root and lint did not exist in agentex/Makefile.
• Adds lint / lint-fix to agentex/Makefile (ruff check + format --check, the same commands CLAUDE.md documents) and root lint / test targets that delegate to agentex/.
• Applies the mechanical ruff fixes the new target surfaced on main (one un-sorted import block, four unformatted files). No behaviour change.

Why

A first-time contributor following CONTRIBUTING hits a wrong clone URL and a missing make target before writing any code.

Test

• make lint at the root and in agentex/: "All checks passed!", 177 files already formatted.
• python -m compileall on the five touched files.
• Note: backend ruff is not run in CI, which is how the drift accumulated; happy to add a CI step in a follow-up if wanted.

https://claude.ai/code/session_01HCVKnA7LeJZ44nxZz1uzF3

Confidence Score: 4/5

The PR appears safe to merge, with two non-blocking lint-entrypoint consistency issues worth correcting.

Summary

• Root commands now delegate backend linting and testing to agentex/.
• Contributor instructions now use the correct repository name and document separate UI checks.
• The new lint entrypoint currently has a narrower scope than the repository Ruff configuration and inaccurately describes its relationship to CI.

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