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.MediaEncoding.Keyframes.Tests/FfProbe/FfProbeKeyframeExtractorTests.cs

@@ -2,10 +2,11 @@
 // Copyright (c) PlaceholderCompany. All rights reserved.
 // </copyright>
 
-namespace Jellyfin.MediaEncoding.Keyframes.FfProbe
+namespace Jellyfin.MediaEncoding.Keyframes.Tests.FfProbe
 {
     using System.IO;
     using System.Text.Json;
+    using Jellyfin.MediaEncoding.Keyframes.FfProbe;
     using Xunit;
 
     public class FfProbeKeyframeExtractorTests
@@ -13,7 +14,9 @@ namespace Jellyfin.MediaEncoding.Keyframes.FfProbe
         [Theory]
         [InlineData("keyframes.txt", "keyframes_result.json")]
         [InlineData("keyframes_streamduration.txt", "keyframes_streamduration_result.json")]
+#pragma warning disable CA1707 // Identifiers should not contain underscores - xUnit test naming convention
         public void ParseStream_Valid_Success(string testDataFileName, string resultFileName)
+#pragma warning restore CA1707
         {
             var testDataPath = Path.Combine("FfProbe/Test Data", testDataFileName);
             var resultPath = Path.Combine("FfProbe/Test Data", resultFileName);