feat: Add useCourse composable for course data management and a new discovery page.

Frontend-Learner/composables/useCourse.ts

@@ -138,6 +138,19 @@ export const useCourse = () => {
             }
         } catch (err: any) {
             console.error('Enroll course failed:', err)
+            
+            // Check for 409 Conflict (Already Enrolled)
+            // ofetch/h3 error properties might vary, check common ones
+            const status = err.statusCode || err.status || err.response?.status
+            
+            if (status === 409) {
+                return {
+                    success: false,
+                    error: 'ท่านได้ลงทะเบียนไปแล้ว',
+                    code: 409
+                }
+            }
+
             return {
                 success: false,
                 error: err.data?.message || err.message || 'Error enrolling in course',

Frontend-Learner/pages/browse/discovery.vue

@@ -86,12 +86,6 @@ const handleEnroll = async (id: number) => {
   if (res.success) {
     // Navigate to my-courses where the success modal will be shown
     return navigateTo('/dashboard/my-courses?enrolled=true');
-  } else if (res.code === 409) {
-     // Already enrolled, maybe redirect to course learning page or my-courses?
-     // For now, let's redirect to my-courses as well, maybe with a different param or just same.
-     // User requirement didn't specify distinct behavior for 409 in UI terms, 
-     // but 'Already enrolled' implies they should go see it.
-     return navigateTo('/dashboard/my-courses');
   } else {
     alert(res.error || 'Failed to enroll');
   }