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.

docs/events/samples/scheduler.rescan.delta@1.sample.json

@@ -0,0 +1,20 @@
+{
+  "eventId": "51d0ef8d-3a17-4af3-b2d7-4ad3db3d9d2c",
+  "kind": "scheduler.rescan.delta",
+  "tenant": "tenant-acme-solar",
+  "ts": "2025-10-18T15:40:11+00:00",
+  "payload": {
+    "impactedDigests": [
+      "sha256:0f0a8de5c1f93d6716b7249f6f4ea3a8db451dc3f3c3ff823f53c9cbde5d5e8a",
+      "sha256:ab921f9679dd8d0832f3710a4df75dbadbd58c2d95f26a4d4efb2fa8c3d9b4ce"
+    ],
+    "reason": "policy-change:scoring/v2",
+    "scheduleId": "rescan-weekly-critical",
+    "summary": {
+      "newCritical": 0,
+      "newHigh": 1,
+      "total": 4
+    }
+  },
+  "attributes": {}
+}