Refactor global configuration page and navigation; add media library page; enhance streamer configuration with detailed options

- Removed the global configuration form and redirected to the consolidated settings page.
- Updated the dashboard to provide feedback when no streamers are configured and added edit links for each streamer.
- Introduced a new media library page to display media files from the configured archive root.
- Enhanced the streamer configuration page with additional options for overrides and settings, including a confirmation modal for deletion.
- Updated the layout and styles for improved user experience and navigation.
- Switched from file-based password storage to database-backed user credentials management in AuthService.
- Applied EF migrations on application startup to ensure database schema is up-to-date.

dotnet/src/TwitchArchive.Core/Persistence/Models/UserCredential.cs

@@ -0,0 +1,8 @@
+namespace TwitchArchive.Core.Persistence.Models
+{
+    public class UserCredential
+    {
+        public int Id { get; set; }
+        public string PasswordHash { get; set; } = string.Empty;
+    }
+}