feat(ui): add proxy during profile creation

[anhtahaylove]

Summary

• add an optional inline proxy field to the new-profile editor
• reuse the existing proxy parser/save/bind commands
• prevent duplicate submits and roll back newly created records when profile setup fails

Scope

• frontend only (src/App.tsx, src/App.css)
• no browser engine, fingerprint, or profile-isolation changes
• no new dependencies

Validation

• npm ci
• npm run build (TypeScript + Vite 5.4.21 production build)
• git diff --check

Closes #27