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.

samples/api/scheduler/impact-set.json

@@ -0,0 +1,34 @@
+{
+  "schemaVersion": "scheduler.impact-set@1",
+  "selector": {
+    "scope": "all-images",
+    "tenantId": "tenant-alpha",
+    "namespaces": [],
+    "repositories": [],
+    "digests": [],
+    "includeTags": [],
+    "labels": [],
+    "resolvesTags": false
+  },
+  "images": [
+    {
+      "imageDigest": "sha256:f1e2d3",
+      "registry": "registry.internal",
+      "repository": "app/api",
+      "namespaces": [
+        "team-a"
+      ],
+      "tags": [
+        "prod"
+      ],
+      "usedByEntrypoint": true,
+      "labels": {
+        "env": "prod"
+      }
+    }
+  ],
+  "usageOnly": true,
+  "generatedAt": "2025-10-18T22:02:58+00:00",
+  "total": 412,
+  "snapshotId": "impact-20251018-1"
+}