[auth-payment-login-lockout] Make auth intro a clean screen with a back button

App Review rejected the 2026-08 build: tapping checkout as a guest
switched root to .auth, which replaced the whole UI with LoginView as the
NavigationStack root - no nav bar, no back, no dismiss. User was trapped.

- LoginView: rebuilt as a static screen in LCENavigationView with a back
  button that sets root = .main, a 'Criar conta' and an 'Entrar' button,
  and 'Termos de Uso' / 'Politica de Privacidade' links. Added #Preview.
- Forced .preferredColorScheme(.light) and fixed DS colors (the app has
  no dark theme, so system dark mode was inverting the nav bar / title).
- Removed the entry-reveal animation machinery (heroVisible/textVisible/
  buttonVisible/token/prepare flags across LoginView, AuthFlowView,
  ContentView) - dead since guest browsing shipped and the root cause of
  the 2026-08-06 'content stuck hidden' bug.
- enterAuthFlow() is now just root = .auth.
- UITestSupport.ensureLoggedIn taps 'Entrar' (new label).
- ProfileLoggedOutFlowTests: new test covering the choices and the way
  back out of .auth.
- Localizable.xcstrings: catalog caught up to the new/removed strings.

PediFoodsUITests/UITestSupport.swift

@@ -147,7 +147,7 @@ extension XCUIApplication {
 
         buttons["Entrar ou Cadastrar"].tap()
 
-        let entrarButton = buttons["ENTRAR"]
+        let entrarButton = buttons["Entrar"]
         guard entrarButton.waitForExistence(timeout: 5) else { return false }
         entrarButton.tap()