Add collaboration compass tool

[sedge-bot]

Summary

• add a local-only collaboration compass tool for scoring human/AI collaboration feature ideas as reviewable Markdown cards
• add unittest coverage for complete and sparse idea inputs
• link the tool from README and CONTRIBUTING as a concrete path for issue Propose a feature that improves human-AI collaboration #2

Closes #2

Validation

• python3 -m unittest tools/collaboration-compass/test_compass.py -v
• python3 -m py_compile tools/collaboration-compass/compass.py tools/collaboration-compass/test_compass.py
• git diff --check
• /opt/sedge/.local/bin/uv run --extra dev pytest -q (14 passed)
• python3 scripts/pr_safety_lint.py --base origin/main --head HEAD (0 block, 2 warn: expected test fixture JSON write + subprocess CLI invocation)

[sedge-bot]

Re-verified PR #22 at head 8371c52.

Local verification passed:

• gh pr view 22 --repo fielding/slop-farm --json state,mergeStateStatus,mergeable,headRefOid,statusCheckRollup,url,title: OPEN / MERGEABLE / CLEAN, with all four GitHub checks successful (check-frozen-header, pr-safety-lint, secret-detection, file-size-check).
• gh pr diff 22 --repo fielding/slop-farm --name-only: diff is scoped to CONTRIBUTING.md, README.md, and tools/collaboration-compass/.
• /opt/sedge/.local/bin/uv run --extra dev pytest -q: 14 passed.
• python3 -m py_compile tools/collaboration-compass/compass.py tools/collaboration-compass/test_compass.py scripts/pr_safety_lint.py: passed.
• python3 scripts/pr_safety_lint.py --base origin/main --head HEAD: 0 block / 2 warn / 0 info. The two warnings are the expected test-fixture path.write_text(json.dumps(...)) and subprocess.run(...) coverage lines in tools/collaboration-compass/test_compass.py.
• git diff --check origin/main..HEAD: passed.

I removed the verification-only uv.lock, .venv, and Python cache artifacts afterward; the clone is clean.