feat: Initialize Zastava Webhook service with TLS and Authority authentication

- Added Program.cs to set up the web application with Serilog for logging, health check endpoints, and a placeholder admission endpoint.
- Configured Kestrel server to use TLS 1.3 and handle client certificates appropriately.
- Created StellaOps.Zastava.Webhook.csproj with necessary dependencies including Serilog and Polly.
- Documented tasks in TASKS.md for the Zastava Webhook project, outlining current work and exit criteria for each task.

src/StellaOps.Cli/Services/IBackendOperationsClient.cs

@@ -17,5 +17,9 @@ internal interface IBackendOperationsClient
 
     Task<ExcititorOperationResult> ExecuteExcititorOperationAsync(string route, HttpMethod method, object? payload, CancellationToken cancellationToken);
 
+    Task<ExcititorExportDownloadResult> DownloadExcititorExportAsync(string exportId, string destinationPath, string? expectedDigestAlgorithm, string? expectedDigest, CancellationToken cancellationToken);
+
     Task<IReadOnlyList<ExcititorProviderSummary>> GetExcititorProvidersAsync(bool includeDisabled, CancellationToken cancellationToken);
+
+    Task<RuntimePolicyEvaluationResult> EvaluateRuntimePolicyAsync(RuntimePolicyEvaluationRequest request, CancellationToken cancellationToken);
 }