feat: Update dialog styles and background colors for consistency across screens

lib/screens/home_screen.dart

@@ -935,6 +935,11 @@ class _CategoryDialogState extends State<_CategoryDialog> {
     final bool? confirm = await showDialog<bool>(
       context: context,
       builder: (BuildContext context) => AlertDialog(
+        backgroundColor: AppColors.cardBackground,
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.circular(12),
+          side: BorderSide(color: AppColors.border),
+        ),
         title: const Text('Borrar categoría'),
         content: const Text('¿Seguro que quieres borrar esta categoría?'),
         actions: [
@@ -943,6 +948,7 @@ class _CategoryDialogState extends State<_CategoryDialog> {
             child: const Text('Cancelar'),
           ),
           TextButton(
+            style: TextButton.styleFrom(foregroundColor: AppColors.destructive),
             onPressed: () => Navigator.pop(context, true),
             child: const Text('Borrar'),
           ),
@@ -957,12 +963,14 @@ class _CategoryDialogState extends State<_CategoryDialog> {
     try {
       await widget.repository.deleteCategory(widget.category!.id);
       await widget.onCategoriesChanged();
-      try {
-        await widget.onRequestSync();
-      } catch (_) {}
+      // Notify parent to switch view to all notes when a category is deleted.
+      await widget.onCategoryDeleted();
       if (mounted) {
         Navigator.pop(context);
       }
+      try {
+        await widget.onRequestSync();
+      } catch (_) {}
     } catch (e) {
       if (mounted) {
         ScaffoldMessenger.of(context).showSnackBar(
@@ -975,6 +983,11 @@ class _CategoryDialogState extends State<_CategoryDialog> {
   @override
   Widget build(BuildContext context) {
     return AlertDialog(
+      backgroundColor: AppColors.cardBackground,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(12),
+        side: BorderSide(color: AppColors.border),
+      ),
       title: Text(
         widget.category == null ? 'Crear categoría' : 'Editar categoría',
       ),

lib/screens/note_editor_screen.dart

@@ -202,7 +202,11 @@ class _NoteEditorScreenState extends State<NoteEditorScreen> {
     final bool isDeletedNote = _currentNote.isDeleted;
 
     return AlertDialog(
-      backgroundColor: AppColors.surfaceElevated,
+      backgroundColor: AppColors.cardBackground,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(12),
+        side: BorderSide(color: AppColors.border),
+      ),
       title: Text(
         isDeletedNote ? 'Eliminar permanentemente' : 'Eliminar nota',
         style: const TextStyle(color: AppColors.textPrimary),

lib/screens/settings_screen.dart

@@ -43,6 +43,11 @@ class _SettingsScreenState extends State<SettingsScreen> {
     final bool? confirmed = await showDialog<bool>(
       context: context,
       builder: (context) => AlertDialog(
+        backgroundColor: AppColors.cardBackground,
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.circular(12),
+          side: BorderSide(color: AppColors.border),
+        ),
         title: const Text('Borrar todos los datos'),
         content: const Text(
           '¿Estás seguro? Esta acción eliminará la base de datos local y la clave de cifrado. Asegúrate de tener una copia de seguridad si es necesario o cuenta sincronizada.',
@@ -96,6 +101,11 @@ class _SettingsScreenState extends State<SettingsScreen> {
     final bool? confirmed = await showDialog<bool>(
       context: context,
       builder: (context) => AlertDialog(
+        backgroundColor: AppColors.cardBackground,
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.circular(12),
+          side: BorderSide(color: AppColors.border),
+        ),
         title: const Text('Borrar toda la info del servidor'),
         content: const Text(
           '¿Estás seguro? Esta acción eliminará toda la información almacenada en el servidor y no se puede deshacer.',