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.

backend/src/repositories/resultRepo.ts

@@ -110,3 +110,62 @@ export function countResultsByUser(userId: number): number {
   const row = db.prepare('SELECT COUNT(*) AS cnt FROM exam_results WHERE user_id = ?').get(userId) as { cnt: number }
   return row.cnt
 }
+
+export function getResultsWithExamJson(userId: number, limit = 100): Array<{
+  title: string
+  score_points: number
+  total_points: number
+  correct_count: number
+  graded_count: number
+  completed_at: number
+  exam_json: string
+  exam_id: number | null
+}> {
+  const db = getDb()
+  return db.prepare(`
+    SELECT title, score_points, total_points, correct_count, graded_count, completed_at, exam_json, exam_id
+    FROM exam_results
+    WHERE user_id = ?
+    ORDER BY completed_at DESC
+    LIMIT ?
+  `).all(userId, limit) as Array<{
+    title: string
+    score_points: number
+    total_points: number
+    correct_count: number
+    graded_count: number
+    completed_at: number
+    exam_json: string
+    exam_id: number | null
+  }>
+}
+
+export interface ScoreTrend {
+  completed_at: number
+  score_pct: number
+  title: string
+  exam_id: number | null
+}
+
+export function getScoreTrends(userId: number, limit = 30): Array<{
+  completed_at: number
+  score_points: number
+  total_points: number
+  title: string
+  exam_id: number | null
+}> {
+  const db = getDb()
+  return db.prepare(`
+    SELECT completed_at, score_points, total_points, title, exam_id
+    FROM exam_results
+    WHERE user_id = ? AND total_points > 0
+    ORDER BY completed_at ASC
+    LIMIT ?
+  `).all(userId, limit) as Array<{
+    completed_at: number
+    score_points: number
+    total_points: number
+    title: string
+    exam_id: number | null
+  }>
+}