feat: expand retrieval eval text report details

[cafitac]

Summary

• Expand retrieval eval text reports with per-failed-task query, missing/avoid IDs, baseline status, and delta details
• Add baseline weak spot and current-vs-baseline regression sections for comparator triage
• Update README and current handoff to describe the richer text report surface

Test Plan

• TMPDIR=/Users/reddit/Project/agent-memory/.tmp-test uv run pytest tests/test_retrieval_evaluation.py::test_render_retrieval_eval_text_report_shows_failed_task_details tests/test_retrieval_evaluation.py::test_render_retrieval_eval_text_report_shows_baseline_weak_spots tests/test_retrieval_evaluation.py::test_render_retrieval_eval_text_report_summarizes_passes_and_type_rollups -q
• TMPDIR=/Users/reddit/Project/agent-memory/.tmp-test uv run pytest tests/test_retrieval_evaluation.py tests/test_cli.py -q
• TMPDIR=/Users/reddit/Project/agent-memory/.tmp-test uv run pytest tests/ -q
• uv run python scripts/check_release_metadata.py
• uv run python scripts/smoke_release_readiness.py