Mirador UI v1.2 — Industrial polish

Changes since v1.1:

Docs & narrative
* README.md + README.fr.md — full French translation + EN/FR switch
* Shared slogan "Watch. Understand. Act." / "Observer. Comprendre. Agir."
  with the "Built with the right tools and the right methods." sub
* Banner SVG redesigned — simpler, more artistic (no word cloud)

CI / release
* GitHub Actions: CodeQL + OSSF Scorecard with workflow_dispatch
* readme-i18n-sync pre-commit hook (lefthook)
* Dropped github-mirror CI job — mirror push now via bin/ship.sh --wait
  (free-org deploy keys blocked by GitHub policy)
* GITHUB_MIRROR_SSH_KEY CI variable kept as placeholder

GitHub org migration
* Beennnn/mirador-ui → mirador1/mirador-ui
* URL rewrites across README, .gitlab-ci.yml, bin/ship.sh, docs

Paired release with mirador-service v1.2.