Add Evidence Graph paired A/B pilot

[GiulioDER]

Summary

• add a deterministic paired Evidence Graph V1 pilot runner
• include baseline, deterministic graph, shuffled relation, removed relation, authored, and proposal-only arms
• fix shuffled relation controls to rewire endpoints while preserving degree distributions
• add pilot tests for routing gains, trust rejection, determinism, and control validity

Validation

• python -m benchmarks.evidence_graph_pilot
• python -m pytest -q tests/test_evidence_graph_eval.py tests/test_evidence_graph_pilot.py tests/test_semantic_graph.py tests/test_semantic_graph_db.py
• 13 passed, 3 skipped
• ruff check passed

The pilot is explicitly directional: it measures evidence routing over a labeled fixture, not end-to-end answer quality.