Add integration and unit tests for Notes API with PostgreSQL-based test hosting configuration

Freman.Sample.Web.IntegrationTests/TestHost/IntegrationTestCollection.cs

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+namespace Freman.Sample.Web.IntegrationTests.TestHost;
+
+[CollectionDefinition(Name, DisableParallelization = true)]
+public sealed class IntegrationTestCollection : ICollectionFixture<IntegrationTestFixture>
+{
+    public const string Name = "Integration tests";
+}

Freman.Sample.Web.IntegrationTests/TestHost/IntegrationTestFixture.cs

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+using Freman.Sample.Web.Data;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Testcontainers.PostgreSql;
+
+namespace Freman.Sample.Web.IntegrationTests.TestHost;
+
+public sealed class IntegrationTestFixture : WebApplicationFactory<Program>, IAsyncLifetime
+{
+    private readonly PostgreSqlContainer _pg = new PostgreSqlBuilder("postgres:16")
+        .WithDatabase("testdb")
+        .WithUsername("appuser")
+        .WithPassword("testpassword")
+        .Build();
+
+    public SampleWebFactory Factory { get; private set; } = null!;
+
+    public async ValueTask InitializeAsync()
+    {
+        await _pg.StartAsync();
+
+        Factory = new SampleWebFactory(_pg.GetConnectionString());
+
+        // Apply migrations once
+        using var scope = Factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+        await db.Database.MigrateAsync();
+    }
+
+    public new async ValueTask DisposeAsync()
+    {
+        await Factory.DisposeAsync();
+        await _pg.DisposeAsync();
+    }
+
+    public async Task ResetDatabaseAsync()
+    {
+        using var scope = Factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+        await db.Database.ExecuteSqlRawAsync(@"TRUNCATE TABLE notes RESTART IDENTITY;");
+    }
+}

Freman.Sample.Web.IntegrationTests/TestHost/SampleWebFactory.cs

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+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Extensions.Configuration;
+
+namespace Freman.Sample.Web.IntegrationTests.TestHost;
+
+public sealed class SampleWebFactory(string connectionString) : WebApplicationFactory<Program>
+{
+    protected override void ConfigureWebHost(IWebHostBuilder builder)
+    {
+        builder.UseEnvironment("Testing");
+
+        builder.ConfigureAppConfiguration((_, config) =>
+        {
+            var overrides = new Dictionary<string, string?>
+            {
+                ["ConnectionStrings:AppDb"] = connectionString,
+                ["ApplyMigrationsOnStartup"] = "false"
+            };
+
+            config.AddInMemoryCollection(overrides);
+        });
+    }
+}