fix(driver): show invalid route upload errors on upload page

[hir-al-14]

Summary

• Invalid route uploads now show a clear error on /upload-route instead of sending drivers to the deprecated driver_assist tester upload screen.
• The old in-page Driver Assist JSON upload fallback has been removed.

Motivation

• Drivers should see upload failures on the page where they selected the route file so they can retry immediately.
• Before this change, invalid JSON or invalid route-shaped JSON was only detected after navigating to /driver_assist, which exposed an old unstyled fallback upload UI.

Changes

• Frontend:

  • Added shared /upload-route validation that parses and transforms route uploads before navigating.
  • Stores invalid upload errors in session storage and renders them in the existing /upload-route error block.
  • Redirects Driver Assist import failures back to /upload-route instead of rendering the deprecated fallback screen.
  • Removed the deprecated Driver Assist direct-upload fallback path, unused file input state, import handler, and related styles.
  • Added regression coverage for rejecting invalid upload-route files before handing them to Driver Assist.

• Backend: No backend changes.

Validation

Frontend

• npm.cmd --prefix app/ui run lint
• npm.cmd --prefix app/ui run format:check
• npm.cmd --prefix app/ui run typecheck
• npm.cmd --prefix app/ui run test
• npm.cmd --prefix app/ui run build
• npm.cmd --prefix app/mobile run lint
• npm.cmd --prefix app/mobile run typecheck

Backend

• cmake --preset dev
• .github/scripts/check-backend-static.sh build/dev
• cmake --build --preset dev --parallel
• ctest --preset dev --output-on-failure --no-tests=error -LE 'e2e|docker'

Risk

• Main behavior change is limited to the Driver Assist route upload/import flow.
• Valid route files still import and navigate to /driver_assist.
• Invalid files now stop on /upload-route with the existing styled error UI.

Rollout and Recovery

• Roll out normally with the frontend deploy.
• If anything looks wrong, revert this PR to restore the previous Driver Assist import behavior.

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.

Related Issues

#198

• The deprecated in-page tester upload screen in Driver Assist is removed.
• Uploading an invalid route file via /upload-route shows an error on /upload-route.
• Valid route files still import and navigate to /driver_assist.
• Dead code from the removed fallback path is removed.
• Regression test added for the invalid upload-route error path.