Auth-before-test: identity cookie, /test auth gate, supersede old results, anon opt-out

Iter 4: result snapshot bugfix, favicon, /stats dashboard, /how page ...

- BUGFIX: /api/result now returns categories/calibrated/total_time_s —
  score snapshot stored in new score_json column (auto-migration),
  old rows degrade gracefully
- favicon.svg (brutalist V mark) linked on all pages
- /stats: live dashboard (starts, signed results, avg IQ, integrity line)
- /how: 'How verification works' — Ed25519 explainer for skeptics with
  offline-verify snippet and honest-limits section
- live-verified: all pages 200, full cycle + OG PNG + scoring tests pass

Claim buttons on result page + scoring unit tests ...

- result.html/result.js: Claim via X / Instagram buttons wired to
  /auth/{x,ig}/start, graceful 503 hint until apps are registered
- scripts/test_scoring.py: 17 unit tests (raw_score, sanity_check bot
  flags, IQ bounds, percentile extremes, categories, calibration
  fallback) — all passing

VerIQ v1 MVP: FastAPI backend, 40-task bank, frontend, Ed25519 signing ...

- backend: main.py (API + sessions + rate limit), scoring.py (weighted
  z-score normalization, sanity checks), signing.py (Ed25519 canonical
  payload signing), db.py (SQLite WAL, results + events)
- content: questions.json v1.0.0 (40 original tasks, 4 categories,
  SVG figures), calibration.json placeholder
- frontend: brutalist dark theme, test engine with timer/resume,
  result page with share links, public verify page
- docs: SPEC.md (product + tech spec, milestones)
- smoke-tested: full cycle start->finish->verify, tamper rejection OK