Add results export choice modal

[Gill87]

Summary

• Replace the Results page's standalone Send action with a single Export action that opens a choice modal.
• Let users choose between the existing WhatsApp send flow and the existing JSON export flow.

Motivation

• Addresses feat: Add export overlay #218 by simplifying the Results page actions while preserving both already-built export/send paths.

Changes

• Frontend: add ExportMethodModal with inline SVG glyphs for WhatsApp and JSON export choices.
• Frontend: route the Results page Export action through the new choice modal, then open SendRoutesModal or ExportRoutesModal.
• Frontend: remove top-level Send buttons from desktop and mobile Results controls while keeping per-route export behavior unchanged.
• Tests: add unit coverage for export method labels and Playwright coverage for the desktop/mobile export-choice flow.

Validation

Frontend

• npm --prefix app/ui run lint
  • Passed with eslint --max-warnings=0.
• npm --prefix app/ui run format:check
  • Passed: all matched files use Prettier style.
• npm --prefix app/ui run typecheck
  • Passed with tsc --noEmit.
• npm --prefix app/ui run test
  • Passed: 24 files, 115 tests.
• npm --prefix app/ui run build
  • Not run; change is limited to client-side Results UI and was covered by typecheck, lint, unit tests, and targeted browser flow.
• npm --prefix app/mobile run lint
  • Not run; mobile app is out of scope for this frontend web-only change.
• npm --prefix app/mobile run typecheck
  • Not run; mobile app is out of scope for this frontend web-only change.
• npx playwright test tests/e2e/optimize-flow.spec.ts -g "results export opens method choices before existing flows" --reporter=line
  • Passed: 1 Chromium test covering desktop and mobile-width Results controls.

Backend

• cmake --preset dev
  • Not run; backend is out of scope.
• .github/scripts/check-backend-static.sh build/dev
  • Not run; backend is out of scope.
• cmake --build --preset dev --parallel
  • Not run; backend is out of scope.
• ctest --preset dev --output-on-failure --no-tests=error -LE 'e2e|docker'
  • Not run; backend is out of scope.
• docker compose -f deploy/compose/docker-compose.arm64.yml --env-file deploy/env/http-server.arm64.env config
  • Not run; backend/infrastructure is out of scope.

Risk

• Low. The change is limited to Results page action wiring and reuses the existing WhatsApp and JSON modals.
• Main risk is a UI regression in the new modal path; covered by targeted Playwright validation.

Rollout and Recovery

• Roll out with the normal frontend deploy.
• Recovery is to revert this PR, restoring separate Send and Export top-level actions.

High-Signal PR Checklist

• The summary states the user-visible or operational outcome, not just file names.
• The motivation explains why this change is needed now.
• The change list separates frontend, backend, infrastructure, and documentation work where applicable.
• Validation includes exact commands run, relevant output, and any checks intentionally skipped.
• Risks, migrations, feature flags, and rollback steps are called out when relevant.
• Screenshots or request/response examples are included for UI and API behavior changes.
  • Not included; targeted browser test covers the UI flow and no API behavior changed.