v0.1.6 - optional trace export tests

Maintenance evidence release for Codex for OSS review.\n\n- Added tests for optional Overmind span export.\n- Proved local audit JSONL persists without Overmind.\n- Proved mocked Overmind receives expected decision span attributes when configured.\n- Proved /v1/analyze still succeeds and writes local audit when Overmind raises.\n- Synced README verification evidence to 105 passing tests.\n- CI and CodeQL are green on this commit; open code-scanning alerts remain 0.