feat: add collections management and study coach features

- Implemented collection repository with CRUD operations for user collections.
- Created routes for managing collections, including listing, creating, updating, and deleting collections.
- Added sharing functionality for exams, allowing users to share and clone exams.
- Developed a study coach service that analyzes exam results and provides study tips based on weak areas.
- Introduced frontend components for managing collections, sharing exams, and displaying study coach insights.
- Enhanced user experience with loading states and error handling in shared components.

frontend/src/api/examApi.ts

@@ -8,24 +8,85 @@ export interface ExamListItem {
   created_at: number
   updated_at: number
   question_count: number
+  share_token: string | null
+  is_favorite: number
+  tags: string
+  collection_id: number | null
 }
 
 export function listExams(): Promise<ExamListItem[]> {
   return apiFetch('/api/exams')
 }
 
-export function getExam(id: number): Promise<Exam> {
+export function getExam(id: number): Promise<Exam & { tags?: string[] }> {
   return apiFetch(`/api/exams/${id}`)
 }
 
-export function createExam(exam: Exam): Promise<{ id: number; title: string }> {
-  return apiFetch('/api/exams', { method: 'POST', body: JSON.stringify({ exam }) })
+export function createExam(exam: Exam, tags?: string[]): Promise<{ id: number; title: string }> {
+  return apiFetch('/api/exams', { method: 'POST', body: JSON.stringify({ exam, tags }) })
 }
 
-export function updateExam(id: number, exam: Exam): Promise<{ success: boolean }> {
-  return apiFetch(`/api/exams/${id}`, { method: 'PUT', body: JSON.stringify({ exam }) })
+export function updateExam(id: number, exam: Exam, tags?: string[]): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}`, { method: 'PUT', body: JSON.stringify({ exam, tags }) })
 }
 
 export function deleteExam(id: number): Promise<{ success: boolean }> {
   return apiFetch(`/api/exams/${id}`, { method: 'DELETE' })
 }
+
+export function shareExam(id: number): Promise<{ shareToken: string }> {
+  return apiFetch(`/api/exams/${id}/share`, { method: 'POST' })
+}
+
+export function unshareExam(id: number): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}/unshare`, { method: 'POST' })
+}
+
+export function getSharedExam(token: string): Promise<{ title: string; subtitle: string | null; questionCount: number; exam: unknown; shareMode: string }> {
+  return apiFetch(`/api/share/${token}`)
+}
+
+export function cloneSharedExam(token: string): Promise<{ id: number; title: string }> {
+  return apiFetch(`/api/share/${token}/clone`, { method: 'POST' })
+}
+
+export function setFavorite(id: number, isFavorite: boolean): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}/favorite`, { method: 'PATCH', body: JSON.stringify({ isFavorite }) })
+}
+
+export function exportExam(id: number): Promise<Blob> {
+  return fetch(`/api/exams/${id}/export`, {
+    headers: {
+      'Authorization': `Bearer ${localStorage.getItem('brainwave.auth.token') || ''}`,
+    },
+  }).then((res) => {
+    if (!res.ok) throw new Error('Export failed')
+    return res.blob()
+  })
+}
+
+export function duplicateExam(id: number): Promise<{ id: number; title: string }> {
+  return apiFetch(`/api/exams/${id}/duplicate`, { method: 'POST' })
+}
+
+export interface ClonedExamItem {
+  id: number
+  title: string
+  subtitle: string | null
+  created_at: number
+  updated_at: number
+  question_count: number
+  cloned_from_share_token: string
+}
+
+export function listClonedExams(): Promise<ClonedExamItem[]> {
+  return apiFetch('/api/exams/cloned')
+}
+
+export function setShareMode(id: number, mode: 'view' | 'clone'): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}/share-mode`, { method: 'PUT', body: JSON.stringify({ mode }) })
+}
+
+export function batchDelete(ids: number[]): Promise<{ deleted: number }> {
+  return apiFetch('/api/exams/batch-delete', { method: 'POST', body: JSON.stringify({ ids }) })
+}