Task 259: Report Quality Review and Improvements

Status: DONE

Periodic report review as recommended by CLAUDE.md: "Periodically have other Claude Code sessions or Codex review reports for readability/clarity."

External agent review (sonnet) identified 6 issues across priority levels:

Undefined CSS variables: --card-bg, --muted, --link, --text-primary, --text-secondary, --text-muted were used but never defined in :root. This caused invisible text in scenario toggles, tooltip links, and missing backgrounds in verdict boxes. Fixed by adding definitions to :root.
Diagram description contrast: .diagram-description { color: #555 } was near-invisible on the dark background (#0d1117). Changed to var(--muted) (#8b949e) for proper contrast.

Invalid TOC HTML nesting: <ul> was nested directly inside <ul> without a wrapping <li>, producing invalid HTML. Fixed by keeping parent <li> open until after the nested </ul>.
Missing .row-label and .highlight CSS: Comparison table row headers had no visual distinction. Added font-weight and background styles.

Cross-report links: Already properly formatted as clickable markdown links.
Data integrity: All 61 dialogueLineId references valid, all external URLs clickable, all math delimiters balanced.

10 new unit tests: CSS variable definitions (6), diagram-description color, row-label/highlight CSS, TOC nesting validity
All 2,028 TS + 191 E2E tests pass