me-web? 0.4: no network failure takes the app down; mobile data read right; the route on the path

- Every network call returns a result whatever fails, not only the exceptions .NET
  usually throws: on Android the HTTPS client is the platform's own stack, and a network
  switch mid-request throws others. The outside test as a whole cannot throw; sharing the
  link falls back to copying it. A last guard (the UI thread, unobserved tasks, Android's
  raiser) writes errors.log in the app folder and keeps the app running; nothing is sent.
- On mobile data the app no longer probes the operator's gateway as if it were a home
  router: the router card says there is none, a private address on the phone with another
  public one is the operator's address sharing (CGNAT) and is drawn as its shared exit, the
  public IPv4 is held by that exit, and the provider's notes are labelled as being about its
  home lines. These were "router not answering" and "can't tell" on an Iliad phone.
- The route's routers appear as stops on the path's wires: the operator's internal ones
  before its exit, the public ones with their network number towards the internet.
- The download speed is timed after the first quarter of the sample, once the connection
  has ramped up; the path no longer shows the address block's registry country.
- Two new strings, drafted in every language.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

src/MeWeb.App/Services/ErrorLog.cs

@@ -0,0 +1,50 @@
+using Avalonia.Threading;
+
+using MeWeb.Shared;
+
+namespace MeWeb.App.Services;
+
+public static class ErrorLog
+{
+  const long MaxBytes = 256 * 1024;
+  static readonly string FilePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "MeWeb", "errors.log");
+  static readonly Lock Gate = new();
+
+  public static void Watch()
+  {
+    Dispatcher.UIThread.UnhandledException += OnDispatcher;
+    TaskScheduler.UnobservedTaskException += OnUnobserved;
+    AppDomain.CurrentDomain.UnhandledException += OnDomain;
+  }
+
+  public static void Write(Exception error)
+  {
+    if (error is null) return;
+    lock (Gate)
+    {
+      try
+      {
+        Directory.CreateDirectory(Path.GetDirectoryName(FilePath));
+        if (File.Exists(FilePath) && new FileInfo(FilePath).Length > MaxBytes) File.Delete(FilePath);
+        File.AppendAllText(FilePath, $"{DateTimeOffset.UtcNow:O} me-web? {BuildInfo.Version}{Environment.NewLine}{error}{Environment.NewLine}{Environment.NewLine}");
+      }
+      catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
+      {
+      }
+    }
+  }
+
+  static void OnDispatcher(object sender, DispatcherUnhandledExceptionEventArgs e)
+  {
+    Write(e.Exception);
+    e.Handled = true;
+  }
+
+  static void OnUnobserved(object sender, UnobservedTaskExceptionEventArgs e)
+  {
+    Write(e.Exception);
+    e.SetObserved();
+  }
+
+  static void OnDomain(object sender, UnhandledExceptionEventArgs e) => Write(e.ExceptionObject as Exception);
+}