Add ApiFactory test helper + /health sanity test

backend.tests/ApiFactory.cs

@@ -0,0 +1,33 @@
+using System.IO;
+using backend.Data;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace backend.tests;
+
+public class ApiFactory : WebApplicationFactory<Program>
+{
+    private readonly string _dbPath = Path.Combine(Path.GetTempPath(), $"assistant-test-{Guid.NewGuid():N}.db");
+
+    protected override void ConfigureWebHost(IWebHostBuilder builder)
+    {
+        builder.UseEnvironment("Test");
+        builder.ConfigureAppConfiguration((_, cfg) =>
+        {
+            cfg.AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["ConnectionStrings:Default"] = $"Data Source={_dbPath}",
+            });
+        });
+    }
+
+    protected override void Dispose(bool disposing)
+    {
+        base.Dispose(disposing);
+        if (File.Exists(_dbPath))
+            File.Delete(_dbPath);
+    }
+}