refactor: allow simulator to connect to api through auth

VigilCare.Simulator/Client/Models/LoginModels.cs

@@ -0,0 +1,9 @@
+public record SimLoginRequest(string Username, string Password);
+
+public record SimLoginResponse(
+    string AccessToken,
+    DateTimeOffset ExpiresAt,
+    Guid UserId,
+    string Username,
+    string DisplayName,
+    string Role);

VigilCare.Simulator/Client/VigilCareApiClient.cs

@@ -1,3 +1,4 @@
+using System.Net.Http.Headers;
 using System.Net.Http.Json;
 
 public class VigilCareApiClient
@@ -9,6 +10,23 @@ public class VigilCareApiClient
         _http = http;
     }
 
+    public async Task LoginAsync(string username, string password)
+    {
+        var response = await _http.PostAsJsonAsync("/api/v1/auth/login",
+            new SimLoginRequest(username, password));
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var body = await response.Content.ReadAsStringAsync();
+            throw new HttpRequestException(
+                $"Login failed ({(int)response.StatusCode} {response.StatusCode}): {body}");
+        }
+
+        var envelope = await response.Content.ReadFromJsonAsync<ApiResponse<SimLoginResponse>>();
+        var token = envelope!.Data!.AccessToken;
+        _http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
+    }
+
     public async Task<PatientResponse> RegisterPatientAsync(RegisterPatientRequest req)
     {
         var response = await _http.PostAsJsonAsync("/api/v1/patients", req);