v0.3.0 — repeat runs, weekly trend, combined multi-engine PDF

Added

• Repeat runs — --repeat R captures the same question set R times as R ordinary runs sharing
  one group. The dashboard reads a group as one measurement: metrics are aggregated across repeats
  and every KPI card shows a min–max spread instead of a run-over-run delta, so an unstable
  number is visible as unstable.
• Weekly trend rollup — a "By run / By week" toggle on the trend chart (ISO weeks).
• Combined multi-engine PDF — report.generate --engines all (and the dashboard's Download PDF
  in compare mode) exports one document: an engines side-by-side table, then a chapter per engine.
  Engines are never blended into a single cross-engine score.
• Cross-engine comparison panel — an "All engines — compare" option showing every captured
  engine of a brand side by side, with click-through into a single engine.

Changed

• KPI cards now follow the selected lens instead of always showing the blended all row, and carry
  a general/branded/comparative distribution bar, because the three query types have different
  expected appearance rates and the blended average misleads on its own.