Fix Q70 in deploy: build-data.js now assembles Shape-of-Logic from probe_runs

The deploy workflow runs `node scripts/build-data.js` before vite build, which
regenerates experiment.json from the probe_runs source-of-truth and overwrites
the manually-edited version. The previous Q70 commit only included the manual
edit, so the deployed site lost Q70 (kept the phase shell but not the question).

This commit makes build-data.js the source of truth:
- Adds PROBES_PROBE_RUNS scan path (probes/probe_runs/)
- New assembleQ70() function reads shape_of_logic_*.json files and assembles
  the Q70 entry with 4 rounds (R1 examine, R2 contaminated/superseded,
  R3 clean re-run with proof body, R4 sandbox consensus)
- Meta title/totalQuestions now derive from questions.length instead of being
  hardcoded to 69
- Fix: totalResponses changed from const to let so Q70 can increment it
- Build verified: 70/70 questions, 1974 total responses, all 4 Q70 rounds
  populated with 6 models each

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Jamie Nucho