feat: Implement dark mode support across the application

- Added ThemeContext to manage theme state and toggle functionality.
- Updated components to support dark mode styles, including header, dashboard, and home page.
- Enhanced CSS for smooth transitions between light and dark themes.
- Modified authentication context to handle async login operations.
- Improved user experience by preserving theme preference in local storage.
- Refactored login and register pages to handle OAuth tokens and errors more gracefully.

ospabhost/backend/.env

@@ -45,8 +45,10 @@ GITHUB_CLIENT_SECRET=623db1b4285637d328689857f3fc8ae19d84b7f1
 
 YANDEX_CLIENT_ID=d8a889ea467f4d699d1854ac7a4f9b48
 YANDEX_CLIENT_SECRET=e599f43f50274344b3bd9a007692c36b
-VK_CLIENT_ID=your_vk_client_id_here
+
+VK_CLIENT_ID=54255963
 VK_CLIENT_SECRET=your_vk_client_secret_here
+
 # OAuth Callback URL
 OAUTH_CALLBACK_URL=https://api.ospab.host/api/auth