Fix diagnostics fact table controls

[douglasmonsky]

Summary

• widen and pin the diagnostics Fact column so fact names wrap later and remain visible during horizontal scroll
• make top-level diagnostics fact table headers sortable with API-backed sort keys for visible aggregate columns
• extend diagnostics fact sorting to cached, output, cache ratio, and largest-call aggregate fields

Validation

• PYTHONPATH=src .venv/bin/python -m pytest tests/test_dashboard_payload.py tests/test_dashboard_server.py
• for file in src/codex_usage_tracker/plugin_data/dashboard/dashboard*.js; do node --check ""; done
• PYTHONPATH=src .venv/bin/python -m ruff check src/codex_usage_tracker/diagnostic_reports.py src/codex_usage_tracker/store.py tests/test_dashboard_payload.py tests/test_dashboard_server.py
• PYTHONPATH=src .venv/bin/python scripts/check_release.py
• git diff --check
• Browser QA: clicked Diagnostics > Top Diagnostic Facts > Cached sort; verified active cached descending sort, no console warnings/errors, and Fact column stayed pinned while the table scrolled horizontally