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

src/Jellyfin.Database/Jellyfin.Database.Implementations/Entities/LibraryOptionsEntity.cs

@@ -0,0 +1,38 @@
+// <copyright file="LibraryOptionsEntity.cs" company="PlaceholderCompany">
+// Copyright (c) PlaceholderCompany. All rights reserved.
+// </copyright>
+
+namespace Jellyfin.Database.Implementations.Entities;
+
+using System;
+
+/// <summary>
+/// Stores serialized collection-folder library options for database-backed persistence.
+/// </summary>
+public class LibraryOptionsEntity
+{
+    /// <summary>
+    /// Gets or sets the collection folder path used as the prototype key.
+    /// </summary>
+    public required string LibraryPath { get; set; }
+
+    /// <summary>
+    /// Gets or sets the serialized library options JSON payload.
+    /// </summary>
+    public required string OptionsJson { get; set; }
+
+    /// <summary>
+    /// Gets or sets the schema version for the serialized payload.
+    /// </summary>
+    public int Version { get; set; }
+
+    /// <summary>
+    /// Gets or sets the UTC timestamp when the row was created.
+    /// </summary>
+    public DateTime DateCreated { get; set; }
+
+    /// <summary>
+    /// Gets or sets the UTC timestamp when the row was last modified.
+    /// </summary>
+    public DateTime DateModified { get; set; }
+}