Remove duplicated package data mirror

[benedictbrady]

Summary

• remove the mirrored C-vs-D corpus from src/philosophy_bench/data
• make experiments/c_vs_d/data the only canonical home for the original benchmark data
• simplify path resolution so shared package code defaults to repo-level experiment data
• remove setuptools package-data declarations and stale compatibility-mirror docs/tests

Repo model

• src/philosophy_bench/: shared Python package, CLI, engine, scoring, providers, analysis code
• experiments/<name>/data: experiment-owned scenarios/primers/labels
• experiments/<name>/harness: experiment-specific scripts or notes
• experiments/<name>/results: checked-in public artifacts

Testing

• uv run philosophy-bench scenarios
• uv run ruff check src tests && uv run ruff format --check src tests
• uv run --extra dev pytest -q
• uv build plus clean wheel install smoke: /tmp/philosophy-bench-canonical-wheel/bin/pytest tests/test_data_packaging.py -q
• gitleaks detect --redact -v --exit-code=2 --report-format=sarif --report-path=/tmp/philosophy-bench-canonical-gitleaks.sarif --log-opts="--no-merges --first-parent origin/main..HEAD"