fix: adiciona optional chaining para prevenir erros de undefined

- Corrige acesso a propriedades undefined em story.content.pages
- Adiciona verificações de segurança com optional chaining (?.)
- Implementa fallback para texto quando conteúdo não está disponível
- Previne erros de runtime em:
  - StudentDashboardPage
  - StudentStoriesPage
  - StoryPage

Resolves: #BUG-789

src/pages/student-dashboard/StoryPage.tsx

@@ -334,7 +334,7 @@ export function StoryPage() {
 
       <div className="bg-white rounded-xl shadow-sm border border-gray-200 overflow-hidden">
         {/* Imagem da página atual */}
-        {story.content.pages[currentPage].image && (
+        {story.content?.pages?.[currentPage]?.image && (
           <div className="relative aspect-video">
             <img
               src={story.content.pages[currentPage].image}
@@ -349,7 +349,7 @@ export function StoryPage() {
           
           {/* Texto da página atual */}
           <p className="text-lg text-gray-700 mb-8">
-            {story.content.pages[currentPage].text}
+            {story.content?.pages?.[currentPage]?.text || 'Carregando...'}
           </p>
 
           {/* Gravador de áudio */}

src/pages/student-dashboard/StudentDashboardPage.tsx

@@ -231,7 +231,7 @@ export function StudentDashboardPage() {
                 className="bg-white rounded-xl shadow-sm border border-gray-200 overflow-hidden cursor-pointer hover:shadow-md transition"
                 onClick={() => navigate(`/aluno/historias/${story.id}`)}
               >
-                {story.content.pages[0].image && (
+                {story.content?.pages?.[0]?.image && (
                   <img
                     src={story.content.pages[0].image}
                     alt={story.title}

src/pages/student-dashboard/StudentStoriesPage.tsx

@@ -197,7 +197,7 @@ export function StudentStoriesPage() {
                 className="bg-white rounded-xl shadow-sm border border-gray-200 overflow-hidden cursor-pointer hover:shadow-md transition"
                 onClick={() => navigate(`/aluno/historias/${story.id}`)}
               >
-                {story.content.pages[0].image && (
+                {story.content?.pages?.[0]?.image && (
                   <img
                     src={story.content.pages[0].image}
                     alt={story.title}