feat(mobile): improve login, profile, alerts screens and dark mode background

- Unify login/register into single screen with tab switcher, logo, and themed inputs
- Redesign profile with header card, segmented theme toggle, icon-based menu, and bottom-sheet modals
- Add auth guard to alerts screen showing login prompt instead of 401 error
- Switch ImageBackground to explicit Image+View layering for reliable rendering
- Add dark mode background image switching in root layout
- Add dark mode override for recent-tag in PWA search view

apps/frontend-mobile/app/auth/register.tsx

@@ -1,167 +1,5 @@
-import React, { useState } from 'react';
-import { 
-  View, 
-  Text, 
-  TextInput, 
-  TouchableOpacity, 
-  StyleSheet, 
-  KeyboardAvoidingView,
-  Platform,
-  Alert
-} from 'react-native';
-import { useRouter } from 'expo-router';
-import { register } from '../../services/auth';
-import { useThemeContext } from '../../components/ThemeProvider';
-import { spacing, borderRadius } from '../../constants/theme';
+import { Redirect } from 'expo-router';
 
-export default function RegisterScreen() {
-  const router = useRouter();
-  const { colors } = useThemeContext();
-  const [username, setUsername] = useState('');
-  const [password, setPassword] = useState('');
-  const [confirmPassword, setConfirmPassword] = useState('');
-  const [isLoading, setIsLoading] = useState(false);
-
-  const handleRegister = async () => {
-    if (!username || !password || !confirmPassword) {
-      Alert.alert('Error', 'Por favor completa todos los campos');
-      return;
-    }
-
-    if (password !== confirmPassword) {
-      Alert.alert('Error', 'Las contraseñas no coinciden');
-      return;
-    }
-
-    setIsLoading(true);
-    try {
-      await register(username, password);
-      router.replace('/(tabs)');
-    } catch (error) {
-      Alert.alert('Error', 'No se pudo crear la cuenta');
-    } finally {
-      setIsLoading(false);
-    }
-  };
-
-  return (
-    <KeyboardAvoidingView
-      style={[styles.container, { backgroundColor: colors.background }]}
-      behavior={Platform.OS === 'ios' ? 'padding' : 'height'}
-    >
-      <View style={styles.form}>
-        <Text style={[styles.title, { color: colors.text }]}>Crear Cuenta</Text>
-        <Text style={[styles.subtitle, { color: colors.textSecondary }]}>Regístrate para empezar</Text>
-
-        <View style={styles.inputContainer}>
-          <Text style={[styles.label, { color: colors.text }]}>Usuario</Text>
-          <TextInput
-            style={[styles.input, { backgroundColor: colors.card, color: colors.text }]}
-            value={username}
-            onChangeText={setUsername}
-            placeholder="Elige un usuario"
-            placeholderTextColor={colors.textSecondary}
-            autoCapitalize="none"
-            autoCorrect={false}
-          />
-        </View>
-
-        <View style={styles.inputContainer}>
-          <Text style={[styles.label, { color: colors.text }]}>Contraseña</Text>
-          <TextInput
-            style={[styles.input, { backgroundColor: colors.card, color: colors.text }]}
-            value={password}
-            onChangeText={setPassword}
-            placeholder="Elige una contraseña"
-            placeholderTextColor={colors.textSecondary}
-            secureTextEntry
-          />
-        </View>
-
-        <View style={styles.inputContainer}>
-          <Text style={[styles.label, { color: colors.text }]}>Confirmar Contraseña</Text>
-          <TextInput
-            style={[styles.input, { backgroundColor: colors.card, color: colors.text }]}
-            value={confirmPassword}
-            onChangeText={setConfirmPassword}
-            placeholder="Repite la contraseña"
-            placeholderTextColor={colors.textSecondary}
-            secureTextEntry
-          />
-        </View>
-
-        <TouchableOpacity
-          style={[styles.button, isLoading && styles.buttonDisabled]}
-          onPress={handleRegister}
-          disabled={isLoading}
-        >
-          <Text style={styles.buttonText}>
-            {isLoading ? 'Creando cuenta...' : 'Crear Cuenta'}
-          </Text>
-        </TouchableOpacity>
-
-        <TouchableOpacity
-          style={styles.linkButton}
-          onPress={() => router.back()}
-        >
-          <Text style={[styles.linkText, { color: colors.primary }]}>¿Ya tienes cuenta? Inicia sesión</Text>
-        </TouchableOpacity>
-      </View>
-    </KeyboardAvoidingView>
-  );
+export default function RegisterRedirect() {
+  return <Redirect href="/auth/login" />;
 }
-
-const styles = StyleSheet.create({
-  container: {
-    flex: 1,
-  },
-  form: {
-    flex: 1,
-    justifyContent: 'center',
-    padding: spacing.xl,
-  },
-  title: {
-    fontSize: 28,
-    fontWeight: 'bold',
-    marginBottom: spacing.sm,
-  },
-  subtitle: {
-    fontSize: 16,
-    marginBottom: spacing.xl,
-  },
-  inputContainer: {
-    marginBottom: spacing.md,
-  },
-  label: {
-    fontSize: 14,
-    fontWeight: '500',
-    marginBottom: spacing.xs,
-  },
-  input: {
-    borderRadius: borderRadius.md,
-    padding: spacing.md,
-    fontSize: 16,
-  },
-  button: {
-    backgroundColor: '#7fbf8f',
-    borderRadius: borderRadius.md,
-    padding: spacing.md,
-    alignItems: 'center',
-    marginTop: spacing.md,
-  },
-  buttonDisabled: {
-    opacity: 0.6,
-  },
-  buttonText: {
-    color: '#ffffff',
-    fontSize: 16,
-    fontWeight: '600',
-  },
-  linkButton: {
-    marginTop: spacing.lg,
-    alignItems: 'center',
-  },
-  linkText: {
-    fontSize: 14,
-  },
-});