Expand harness docs, README, and offline verify script

[Abhishek21g]

Problem

Issue #1 — README is minimal and does not explain how to run the harness or reproduce the eval pipeline described in Cognition's SWE-bench technical report.

Fix

• Expand README.md with repo layout, quickstart, and eval summary
• Add docs/HARNESS.md documenting the agent eval pipeline:
  • git remote strip (leakage prevention)
  • test-file reset before grading
  • test_patch apply order
  • fail-to-pass test execution
• Add scripts/verify_harness.py — offline mock validator for harness invariants (no SWE-bench download)
• Add 7 pytest tests + GitHub Actions CI

Verification

python -m venv .venv && source .venv/bin/activate
pip install pytest
pytest tests/test_verify_harness.py -v
python scripts/verify_harness.py --mock --json
python scripts/verify_harness.py --fail-demo   # expect exit 1 (missing test reset)

Closes #1

---

Devin Review

Status	Commit
⚪ Not started	—

Run Devin Review

💡 Connect your GitHub account to enable automatic code reviews.