fix(web): use locale dropdown across authentication flows

[Tutitoos]

Summary

• replace the setup, sign-in, recovery, and auth-error language toggle with an explicit English/Spanish dropdown
• expose accessible radio-menu state and close the menu on selection, outside click, or Escape
• keep the menu above authentication cards on mobile with a Tailwind stacking utility
• extend browser coverage to exercise the menu and locale selection

Validation

• bun run --cwd apps/web test (50 passed)
• bun run --cwd apps/web typecheck
• bun run --cwd apps/web build
• bunx playwright test tests/bootstrap.spec.ts (18 passed across 6 viewports)

Closes #194