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.Scheduler.Storage.Mongo/Migrations/EnsureSchedulerCollectionsMigration.cs

@@ -0,0 +1,47 @@
+using Microsoft.Extensions.Logging;
+using MongoDB.Driver;
+using StellaOps.Scheduler.Storage.Mongo.Internal;
+
+namespace StellaOps.Scheduler.Storage.Mongo.Migrations;
+
+internal sealed class EnsureSchedulerCollectionsMigration : ISchedulerMongoMigration
+{
+    private readonly ILogger<EnsureSchedulerCollectionsMigration> _logger;
+
+    public EnsureSchedulerCollectionsMigration(ILogger<EnsureSchedulerCollectionsMigration> logger)
+        => _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+
+    public string Id => "20251019_scheduler_collections_v1";
+
+    public async ValueTask ExecuteAsync(SchedulerMongoContext context, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+
+        var requiredCollections = new[]
+        {
+            context.Options.SchedulesCollection,
+            context.Options.RunsCollection,
+            context.Options.ImpactSnapshotsCollection,
+            context.Options.AuditCollection,
+            context.Options.LocksCollection,
+            context.Options.MigrationsCollection
+        };
+
+        var cursor = await context.Database
+            .ListCollectionNamesAsync(cancellationToken: cancellationToken)
+            .ConfigureAwait(false);
+
+        var existing = await cursor.ToListAsync(cancellationToken).ConfigureAwait(false);
+
+        foreach (var collection in requiredCollections)
+        {
+            if (existing.Contains(collection, StringComparer.Ordinal))
+            {
+                continue;
+            }
+
+            _logger.LogInformation("Creating Scheduler Mongo collection '{CollectionName}'.", collection);
+            await context.Database.CreateCollectionAsync(collection, cancellationToken: cancellationToken).ConfigureAwait(false);
+        }
+    }
+}