Four fully authenticated endpoints at /api/export/experiments/{id}/:
- /best: Returns best config as JSON with weighted score and metadata
- /env: Flattened KEY=VALUE format with metadata comments
- /yaml: Simple YAML serialization (no external dependency)
- /report: Full markdown report with config space, top N configs,
score distributions, token usage, and timing stats
34 tests in test_export.py covering all endpoints, auth, 404s, and helpers.
Updated test_routers.py to expect 401 (auth required) instead of 501 (stub).
