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.Excititor.Core/VexClaim.cs

@@ -16,6 +16,7 @@ public sealed record VexClaim
         VexJustification? justification = null,
         string? detail = null,
         VexConfidence? confidence = null,
+        VexSignalSnapshot? signals = null,
         ImmutableDictionary<string, string>? additionalMetadata = null)
     {
         if (string.IsNullOrWhiteSpace(vulnerabilityId))
@@ -43,6 +44,7 @@ public sealed record VexClaim
         Justification = justification;
         Detail = string.IsNullOrWhiteSpace(detail) ? null : detail.Trim();
         Confidence = confidence;
+        Signals = signals;
         AdditionalMetadata = NormalizeMetadata(additionalMetadata);
     }
 
@@ -66,6 +68,8 @@ public sealed record VexClaim
 
     public VexConfidence? Confidence { get; }
 
+    public VexSignalSnapshot? Signals { get; }
+
     public ImmutableSortedDictionary<string, string> AdditionalMetadata { get; }
 
     private static ImmutableSortedDictionary<string, string> NormalizeMetadata(