refactor: optimize project structure, migrate to SQLite, and add new features

fix:
  - Fix TypeScript type errors in api-wrapper.ts (ApiResponse type)
  - Fix backward compatibility in database.ts getSettings() for missing fields
  - Fix default value for weekNavigationEnabled (changed from true to false)
  - Fix API routes error handling with unified wrapper
  - Fix duplicate toggle switch code in admin.tsx (6 instances)
  - Fix inconsistent authentication check in API routes (unified with withAuth)
  - Fix error message text in loading-context.tsx (improved user experience)

add:
  - Add database.ts: SQLite database layer with better-sqlite3 for persistent storage
    * Groups management (CRUD operations)
    * Settings management with caching
    * Admin password hashing with bcrypt
    * Automatic database initialization and migration
  - Add api-wrapper.ts utility for unified API route handling
    * withAuth wrapper for protected routes
    * withMethods wrapper for public routes
    * Consistent error handling and method validation
  - Add validation.ts utility with centralized validation functions
    * validateCourse - course validation (1-5)
    * validateGroupId - group ID format validation
    * validatePassword - password strength validation
  - Add showAddGroupButton setting to control visibility of 'Add Group' button on homepage
  - Add toggle switch component in admin.tsx for reusable UI (replaces 6 duplicate instances)
  - Add CourseSelect component in admin.tsx for reusable course selection
  - Add DialogFooterButtons component in admin.tsx for reusable dialog footer
  - Add unified loadData function in admin.tsx to reduce code duplication
  - Add change-password.ts API endpoint for admin password management
  - Add logs.ts API endpoint for viewing error logs in admin panel
  - Add logErrorToFile function in logger.ts for persistent error logging
  - Add comprehensive error logging in schedule.ts (parsing, fetch, timeout, network errors)
  - Add comprehensive project structure documentation in README.md
  - Add architecture and code organization section in README.md
  - Add database information section in README.md
  - Add SQLite and bcrypt to tech stack documentation
  - Add better-sqlite3 and bcrypt dependencies to package.json
  - Add .gitignore rules for error.log and database files (data/, *.db, *.db-shm, *.db-wal)

refactor:
  - Refactor admin.tsx: extract reusable components (toggle, select, dialog footer)
  - Refactor API routes to use withAuth wrapper for consistent authentication
  - Refactor API routes to use validation utilities instead of inline validation
  - Refactor groups.ts and groups.json: move to old/data/ directory (deprecated, now using SQLite)
  - Refactor settings-loader.ts: migrate from JSON to SQLite database
  - Refactor groups-loader.ts: migrate from JSON to SQLite database
  - Refactor database.ts: improve backward compatibility for settings migration
  - Refactor admin.tsx: unify data loading functions (loadGroupsList, loadSettingsList)
  - Refactor index.tsx: add showAddGroupButton prop and conditional rendering
  - Refactor API routes: consistent error handling and method validation
  - Refactor README.md: update tech stack, project structure, and admin panel documentation
  - Refactor auth.ts: improve session management and cookie handling
  - Refactor schedule.ts: improve error handling with detailed logging and error types
  - Refactor logger.ts: add file-based error logging functionality
  - Refactor loading-context.tsx: improve error message clarity

remove:
  - Remove hello.ts test API endpoint
  - Remove groups.ts and groups.json (moved to old/data/, replaced by SQLite)

update:
  - Update .gitignore to exclude old data files, database files, and error logs
  - Update package.json: add better-sqlite3, bcrypt and their type definitions
  - Update README.md with new features, architecture, and database information
  - Update all API routes to use new wrapper system
  - Update admin panel with new settings and improved UI
  - Update sitemap.xml with cache usage comment

src/pages/api/admin/settings.ts

@@ -1,33 +1,37 @@
 import type { NextApiRequest, NextApiResponse } from 'next'
-import { requireAuth } from '@/shared/utils/auth'
-import { loadSettings, saveSettings, AppSettings } from '@/shared/data/settings-loader'
+import { withAuth, ApiResponse } from '@/shared/utils/api-wrapper'
+import { loadSettings, saveSettings, clearSettingsCache, AppSettings } from '@/shared/data/settings-loader'
 
-type ResponseData = {
+type ResponseData = ApiResponse<{
   settings?: AppSettings
-  success?: boolean
-  error?: string
-}
+}>
 
 async function handler(
   req: NextApiRequest,
   res: NextApiResponse<ResponseData>
 ) {
   if (req.method === 'GET') {
-    // Получение настроек
-    const settings = loadSettings()
+    // Получение настроек (всегда свежие данные для админ-панели)
+    clearSettingsCache()
+    const settings = loadSettings(true)
     res.status(200).json({ settings })
     return
   }
 
   if (req.method === 'PUT') {
     // Обновление настроек
-    const { weekNavigationEnabled, debug } = req.body
+    const { weekNavigationEnabled, showAddGroupButton, debug } = req.body
 
     if (typeof weekNavigationEnabled !== 'boolean') {
       res.status(400).json({ error: 'weekNavigationEnabled must be a boolean' })
       return
     }
 
+    if (showAddGroupButton !== undefined && typeof showAddGroupButton !== 'boolean') {
+      res.status(400).json({ error: 'showAddGroupButton must be a boolean' })
+      return
+    }
+
     // Валидация debug опций (только в dev режиме)
     if (debug !== undefined) {
       if (typeof debug !== 'object' || debug === null) {
@@ -51,32 +55,20 @@ async function handler(
 
     const settings: AppSettings = {
       weekNavigationEnabled,
+      showAddGroupButton: showAddGroupButton !== undefined ? showAddGroupButton : true,
       ...(debug !== undefined && { debug })
     }
 
-    try {
-      saveSettings(settings)
-      // Сбрасываем кеш и загружаем свежие настройки для подтверждения
-      const { clearSettingsCache } = await import('@/shared/data/settings-loader')
-      clearSettingsCache()
-      const savedSettings = loadSettings()
-      res.status(200).json({ success: true, settings: savedSettings })
-    } catch (error) {
-      console.error('Error saving settings:', error)
-      res.status(500).json({ error: 'Failed to save settings' })
-    }
+    saveSettings(settings)
+    // Сбрасываем кеш и загружаем свежие настройки для подтверждения
+    clearSettingsCache()
+    const savedSettings = loadSettings(true)
+    res.status(200).json({ success: true, settings: savedSettings })
     return
   }
-
-  res.status(405).json({ error: 'Method not allowed' })
 }
 
-export default function protectedHandler(
-  req: NextApiRequest,
-  res: NextApiResponse<ResponseData>
-) {
-  return requireAuth(req, res, handler)
-}
+export default withAuth(handler, ['GET', 'PUT'])