Merge branch 'feat/self-update'

Self-update for app and installer. Integrates cleanly with the
worker-log-footer feature that landed on main in parallel — the
shell VM now carries both worker-log state and update-check state,
and MainWindow hosts both the update banner and the footer log line.

Conflict resolved in IslandsShellViewModel.cs: kept nullable property
types from main's test-only parameterless constructor work, and added
the UpdateCheck property exposing the injected service.

src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs

@@ -1,4 +1,7 @@
 using Avalonia.Threading;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using ClaudeDo.Data.Models;
@@ -13,6 +16,7 @@ public sealed partial class IslandsShellViewModel : ViewModelBase
     public TasksIslandViewModel? Tasks { get; }
     public DetailsIslandViewModel? Details { get; }
     public WorkerClient? Worker { get; }
+    public UpdateCheckService UpdateCheck => _updateCheck;
 
     public string ConnectionText =>
         Worker?.IsConnected == true ? "Online"
@@ -21,6 +25,14 @@ public sealed partial class IslandsShellViewModel : ViewModelBase
 
     public bool IsOffline => Worker?.IsConnected != true && Worker?.IsReconnecting != true;
 
+    private readonly UpdateCheckService _updateCheck;
+    private readonly InstallerLocator _installerLocator;
+
+    [ObservableProperty] private bool _isUpdateBannerVisible;
+    [ObservableProperty] private string? _updateBannerLatestVersion;
+    [ObservableProperty] private string? _inlineUpdateStatus;
+    private bool _bannerDismissedThisSession;
+
     [ObservableProperty]
     private double _windowWidth = 1280;
 
@@ -79,9 +91,13 @@ public sealed partial class IslandsShellViewModel : ViewModelBase
         ListsIslandViewModel lists,
         TasksIslandViewModel tasks,
         DetailsIslandViewModel details,
-        WorkerClient worker)
+        WorkerClient worker,
+        UpdateCheckService updateCheck,
+        InstallerLocator installerLocator)
     {
         Lists = lists; Tasks = tasks; Details = details; Worker = worker;
+        _updateCheck = updateCheck;
+        _installerLocator = installerLocator;
         Lists.SelectionChanged += (_, _) => Tasks.LoadForList(Lists.SelectedList);
         Tasks.SelectionChanged += (_, _) => Details.Bind(Tasks.SelectedTask);
         Tasks.TasksChanged     += (_, _) => _ = Lists.RefreshCountsAsync();
@@ -109,5 +125,74 @@ public sealed partial class IslandsShellViewModel : ViewModelBase
                 Dispatcher.UIThread.Post(ClearWorkerLog);
         };
         _ = Lists.LoadAsync();
+        _updateCheck.PropertyChanged += (_, e) =>
+        {
+            if (e.PropertyName == nameof(UpdateCheckService.LastCheckStatus))
+            {
+                RefreshBannerFromStatus();
+            }
+        };
+        // Fire-and-forget startup check — never block UI.
+        _ = Task.Run(async () =>
+        {
+            try { await _updateCheck.CheckNowAsync(CancellationToken.None); } catch { }
+        });
+    }
+
+    private void RefreshBannerFromStatus()
+    {
+        switch (_updateCheck.LastCheckStatus)
+        {
+            case UpdateCheckStatus.UpdateAvailable:
+                if (_bannerDismissedThisSession) { IsUpdateBannerVisible = false; break; }
+                UpdateBannerLatestVersion = _updateCheck.LatestVersion;
+                IsUpdateBannerVisible = true;
+                InlineUpdateStatus = null;
+                break;
+            case UpdateCheckStatus.UpToDate:
+                IsUpdateBannerVisible = false;
+                ShowInlineStatus($"You're up to date (v{_updateCheck.CurrentVersion})");
+                break;
+            case UpdateCheckStatus.CheckFailed:
+                ShowInlineStatus("Could not check for updates");
+                break;
+        }
+    }
+
+    private async void ShowInlineStatus(string text)
+    {
+        InlineUpdateStatus = text;
+        await Task.Delay(3000);
+        if (InlineUpdateStatus == text) InlineUpdateStatus = null;
+    }
+
+    [RelayCommand]
+    private async Task CheckForUpdatesAsync()
+    {
+        await _updateCheck.CheckNowAsync(CancellationToken.None);
+    }
+
+    [RelayCommand]
+    private void DismissBanner()
+    {
+        _bannerDismissedThisSession = true;
+        IsUpdateBannerVisible = false;
+    }
+
+    [RelayCommand]
+    private void UpdateNow()
+    {
+        var path = _installerLocator.Find();
+        if (path is null) return;
+
+        try
+        {
+            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(path) { UseShellExecute = true });
+            Environment.Exit(0);
+        }
+        catch
+        {
+            // Intentionally silent — if this fails there's nothing useful to show.
+        }
     }
 }