v0.6.0 — Evidence snapshots and graph integrity

Closes the core validation gaps found in adversarial review.\n\n- rejects malformed and future source dates\n- requires retrievedAt and hashes recorded excerpt snapshots\n- enforces bounded locators and rejects repeated filler\n- rejects duplicate edges, directed cycles, and disconnected reasoning subgraphs\n- fixes claim and contradiction metrics\n- expands the deterministic adversarial benchmark to 20/20 cases\n- makes skill archive digests reproducible across the Node 18/20/22 CI matrix\n- lets the Action exclude intentionally failing benchmark fixtures\n\nAll CI, Evidence contract, and Pages checks passed on the release commit.