feat: add Migrator console project

- Dedicated HrynCo.NotificationService.Migrator console app
- Reads App:ConnectionString from config/env
- Calls db.Database.MigrateAsync() with clear log output
- Own Dockerfile (runtime:10.0 base, no SDK overhead)
- Replaces SDK volume-mount approach in docker-compose
- Added to solution with /docker/Migrator/ folder

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Migrator/Program.cs

@@ -0,0 +1,46 @@
+using HrynCo.NotificationService.DAL.EF;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Serilog;
+
+Log.Logger = new LoggerConfiguration()
+    .WriteTo.Console()
+    .CreateBootstrapLogger();
+
+try
+{
+    Log.Information("🚀 Notification Service Migrator starting...");
+
+    var host = Host.CreateDefaultBuilder(args)
+        .UseSerilog((ctx, cfg) => cfg
+            .ReadFrom.Configuration(ctx.Configuration)
+            .WriteTo.Console())
+        .ConfigureServices((ctx, services) =>
+        {
+            var connectionString = ctx.Configuration["App:ConnectionString"]
+                ?? throw new InvalidOperationException("App:ConnectionString is not configured.");
+
+            services.AddDbContext<NotificationDbContext>(options =>
+                options.UseNpgsql(connectionString));
+        })
+        .Build();
+
+    using var scope = host.Services.CreateScope();
+    var db = scope.ServiceProvider.GetRequiredService<NotificationDbContext>();
+
+    Log.Information("Applying migrations...");
+    await db.Database.MigrateAsync();
+    Log.Information("Migrations applied successfully.");
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "Migration failed.");
+    return 1;
+}
+finally
+{
+    await Log.CloseAndFlushAsync();
+}
+
+return 0;