feat: Implement API modules for admin, auth, exam, result, and setup functionalities

- Created adminApi.ts for admin-related operations including user management and site settings.
- Developed authApi.ts for authentication processes such as registration, login, and profile management.
- Added examApi.ts for handling exam CRUD operations.
- Introduced resultApi.ts for managing results submission and retrieval.
- Established setupApi.ts for initial setup processes and status checks.
- Created ErrorBoundary component to handle rendering errors gracefully in the frontend.
- Re-exported shared API utilities in index.ts for easier access.

backend/src/repositories/resultRepo.ts

@@ -0,0 +1,112 @@
+import { getDb } from '../db/database.js'
+
+export interface DbResult {
+  id: number
+  user_id: number
+  exam_id: number | null
+  title: string
+  score_points: number
+  total_points: number
+  correct_count: number
+  graded_count: number
+  passing_score: number
+  elapsed_ms: number
+  state_json: string
+  exam_json: string
+  completed_at: number
+}
+
+export interface ResultListItem {
+  id: number
+  title: string
+  score_points: number
+  total_points: number
+  correct_count: number
+  graded_count: number
+  passing_score: number
+  elapsed_ms: number
+  completed_at: number
+  exam_id: number | null
+}
+
+export function createResult(data: Omit<DbResult, 'id'>): { id: number } {
+  const db = getDb()
+  const result = db.prepare(`
+    INSERT INTO exam_results (user_id, exam_id, title, score_points, total_points, correct_count, graded_count, passing_score, elapsed_ms, state_json, exam_json)
+    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+  `).run(
+    data.user_id,
+    data.exam_id ?? null,
+    data.title,
+    data.score_points,
+    data.total_points,
+    data.correct_count,
+    data.graded_count,
+    data.passing_score ?? 60,
+    data.elapsed_ms ?? 0,
+    data.state_json,
+    data.exam_json
+  )
+  return { id: result.lastInsertRowid as number }
+}
+
+export function getResultById(id: number, userId: number): DbResult | undefined {
+  const db = getDb()
+  return db.prepare('SELECT * FROM exam_results WHERE id = ? AND user_id = ?').get(id, userId) as DbResult | undefined
+}
+
+export function listResultsByUser(userId: number, options: { limit?: number; offset?: number } = {}): { results: ResultListItem[]; total: number } {
+  const db = getDb()
+  const limit = Math.min(options.limit ?? 30, 100)
+  const offset = options.offset ?? 0
+
+  const results = db.prepare(`
+    SELECT id, title, score_points, total_points, correct_count, graded_count,
+           passing_score, elapsed_ms, completed_at, exam_id
+    FROM exam_results
+    WHERE user_id = ?
+    ORDER BY completed_at DESC
+    LIMIT ? OFFSET ?
+  `).all(userId, limit, offset) as ResultListItem[]
+
+  const countRow = db.prepare('SELECT COUNT(*) AS total FROM exam_results WHERE user_id = ?').get(userId) as { total: number }
+
+  return { results, total: countRow.total }
+}
+
+export function deleteResult(id: number, userId: number): boolean {
+  const db = getDb()
+  const result = db.prepare('DELETE FROM exam_results WHERE id = ? AND user_id = ?').run(id, userId)
+  return result.changes > 0
+}
+
+export function countResults(): number {
+  const db = getDb()
+  const row = db.prepare('SELECT COUNT(*) AS cnt FROM exam_results').get() as { cnt: number }
+  return row.cnt
+}
+
+export function getAverageScore(): number {
+  const db = getDb()
+  const row = db.prepare(
+    'SELECT COALESCE(AVG(score_points * 100.0 / NULLIF(total_points, 0)), 0) AS avg FROM exam_results'
+  ).get() as { avg: number }
+  return Math.round(row.avg * 10) / 10
+}
+
+export function getRecentResults(limit: number): Array<DbResult & { display_name: string; email: string }> {
+  const db = getDb()
+  return db.prepare(`
+    SELECT er.*, u.display_name, u.email
+    FROM exam_results er
+    JOIN users u ON u.id = er.user_id
+    ORDER BY er.completed_at DESC
+    LIMIT ?
+  `).all(limit) as Array<DbResult & { display_name: string; email: string }>
+}
+
+export function countResultsByUser(userId: number): number {
+  const db = getDb()
+  const row = db.prepare('SELECT COUNT(*) AS cnt FROM exam_results WHERE user_id = ?').get(userId) as { cnt: number }
+  return row.cnt
+}