Add detailed analysis and documentation for RSNet.dll download functionality

- Introduced a comprehensive markdown document outlining the API surface of RSNet.dll related to downloading video files.
- Documented initialization, connection, record querying, and download processes.
- Provided insights into the exported functions, their parameters, and expected behaviors.
- Included practical implications and recommendations for implementing a downloader script using C# interop.
- Highlighted the necessary struct layouts and callback mechanisms for effective integration with the DLL.

SurveillanceClient/src/SurveillanceClient.Core/ServiceCollectionExtensions.cs

@@ -0,0 +1,27 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using SurveillanceClient.Core.Configuration;
+using SurveillanceClient.Core.Services;
+
+namespace SurveillanceClient.Core;
+
+/// <summary>
+/// DI registration helpers for the SurveillanceClient Core services.
+/// </summary>
+public static class ServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers <see cref="IRsNetClient"/> and binds its options from
+    /// configuration. The client is a singleton because <c>RSNet.dll</c>
+    /// holds process-wide global state.
+    /// </summary>
+    public static IServiceCollection AddSurveillanceClientCore(this IServiceCollection services)
+    {
+        services.AddOptions<RsNetOptions>().BindConfiguration(RsNetOptions.SectionName);
+        services.AddOptions<DeviceOptions>().BindConfiguration(DeviceOptions.SectionName);
+
+        services.TryAddSingleton<IRsNetClient, RsNetClient>();
+
+        return services;
+    }
+}