Settings, correção de light/darkmode do dispositivo (e adição da escolha entre modos nas settings) e correção do tipo de letra no textfield do chatbot

lib/core/providers/theme_provider.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../services/theme_service.dart';
+
+/// Provider for theme management
+final themeProvider = StateNotifierProvider<ThemeNotifier, ThemeMode>((ref) {
+  return ThemeNotifier();
+});
+
+/// Notifier for managing theme state
+class ThemeNotifier extends StateNotifier<ThemeMode> {
+  ThemeNotifier() : super(ThemeMode.light) {
+    _initializeTheme();
+  }
+
+  /// Initialize theme from storage
+  Future<void> _initializeTheme() async {
+    try {
+      final storedTheme = await ThemeService.getThemeMode();
+      state = storedTheme;
+    } catch (e) {
+      state = ThemeMode.light;
+    }
+  }
+
+  /// Change theme mode
+  Future<void> setThemeMode(ThemeMode themeMode) async {
+    // For now, only allow light mode
+    // Future: Allow dark mode when available
+    if (themeMode == ThemeMode.light || ThemeService.isDarkModeAvailable()) {
+      state = themeMode;
+      await ThemeService.setThemeMode(themeMode);
+    }
+  }
+
+  /// Toggle between light and dark mode (for future use)
+  Future<void> toggleTheme() async {
+    if (ThemeService.isDarkModeAvailable()) {
+      final newTheme = state == ThemeMode.light
+          ? ThemeMode.dark
+          : ThemeMode.light;
+      await setThemeMode(newTheme);
+    }
+  }
+
+  /// Reset to default theme
+  Future<void> resetTheme() async {
+    await setThemeMode(ThemeMode.light);
+  }
+
+  /// Check if current theme is dark
+  bool isDarkMode() {
+    return state == ThemeMode.dark;
+  }
+
+  /// Check if current theme is light
+  bool isLightMode() {
+    return state == ThemeMode.light;
+  }
+
+  /// Get current theme as string
+  String get currentThemeString {
+    return ThemeService.getThemeModeString(state);
+  }
+
+  /// Initialize theme from storage (for future use)
+  Future<void> initializeTheme() async {
+    final storedTheme = await ThemeService.getStoredThemeMode();
+    // Only set if dark mode is available or if it's light mode
+    if (storedTheme == ThemeMode.light || ThemeService.isDarkModeAvailable()) {
+      state = storedTheme;
+    }
+  }
+}
+
+/// Provider for checking if dark mode is available
+final isDarkModeAvailableProvider = Provider<bool>((ref) {
+  return ThemeService.isDarkModeAvailable();
+});
+
+/// Provider for current theme string
+final themeStringProvider = Provider<String>((ref) {
+  final theme = ref.watch(themeProvider);
+  return ThemeService.getThemeModeString(theme);
+});