feat: SMS OTP auth + phone verification gate + improved login UI
- Usuario model: add isPhoneVerified field from is_phone_verified
- auth_provider.dart: fix access_token key, add _navigateAfterAuth gate
(redirects to phoneLoginRoute if phone not verified), add verifyPhoneNumber,
signInWithOTP, verifyPhoneNumberForLink, linkPhoneWithOTP methods
- phone_login_view.dart: full rewrite with logo, +57 prefix, two-step OTP flow
(phone input → code input), 60s resend timer, email login fallback
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>