Add JSON config, DB-backed library options, and docs

- Add JSON-based config loading with XML fallback for DB and library options
- Implement LibraryOptionsRepository with EF Core, migrations, and entity
- Update CollectionFolder to use DB-backed options with XML fallback/backfill
- Register repository in DI and initialize at startup
- Use EF execution strategy for transactional DB operations
- Suppress code analysis warnings in .csproj and test files
- Add DATABASE_MIGRATION.md, LIBRARY_OPTIONS_DB_DESIGN.md, and WEBSOCKET_AUTHENTICATION.md
- Add database.json.example and improve migration docs
- Add tests for JSON config loader and update test naming warnings

tests/Jellyfin.Extensions.Tests/Json/Converters/JsonCommaDelimitedIReadOnlyListTests.cs

@@ -2,6 +2,8 @@
 // Copyright (c) PlaceholderCompany. All rights reserved.
 // </copyright>
 
+#pragma warning disable CA1707 // Identifiers should not contain underscores - xUnit test naming convention
+
 namespace Jellyfin.Extensions.Tests.Json.Converters
 {
     using System.Text.Json;
@@ -129,3 +131,5 @@ namespace Jellyfin.Extensions.Tests.Json.Converters
         }
     }
 }
+
+#pragma warning restore CA1707