feat(ui): merge action and robust jump-to-task in worktrees overview

Add Merge entry to the worktrees overview context menu wiring the existing
MergeModalViewModel, replace fire-and-forget list selection with a
collection-change-aware JumpToTaskHelper, and propagate list renames to
visible task rows via a new ListUpdated event.

Harden worktree state changes: WorkerHub.SetWorktreeState now rejects
invalid transitions, WorktreeMaintenanceService only drops the DB row when
the on-disk worktree was actually removed, and Cleanup/Reset broadcast
WorktreeUpdated for affected tasks. SetWorktreeStateAsync returns the hub
error message so the modal can surface it.

Also: de-duplicate the worktrees overview modal opener, hook
OnParentTaskIdChanged to refresh IsDraft, fix MergeModal CanExecute
notifications, and add WorktreeStateHubTests for the transition rules.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/Hub/WorktreeStateHubTests.cs

@@ -0,0 +1,107 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Microsoft.AspNetCore.SignalR;
+using Xunit;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Hub;
+
+public sealed class WorktreeStateHubTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+
+    public void Dispose() => _db.Dispose();
+
+    private WorkerHub CreateHub()
+    {
+        var broadcaster = new HubBroadcaster(new CapturingHubContext());
+        var hub = new WorkerHub(
+            null!, null!, null!, null!, broadcaster, _db.CreateFactory(),
+            null!, null!, null!, null!, null!, null!, null!, null!, null!, null!);
+        hub.Clients = new FakeHubCallerClients(new RecordingClientProxy());
+        hub.Context = new FakeHubCallerContext();
+        return hub;
+    }
+
+    private async Task<string> SeedWorktreeAsync(WorktreeState initial)
+    {
+        using var ctx = _db.CreateContext();
+        var listId = Guid.NewGuid().ToString();
+        var taskId = Guid.NewGuid().ToString();
+        await new ListRepository(ctx).AddAsync(new ListEntity
+        {
+            Id = listId, Name = "L", CreatedAt = DateTime.UtcNow,
+        });
+        await new TaskRepository(ctx).AddAsync(new TaskEntity
+        {
+            Id = taskId, ListId = listId, Title = "T",
+            Status = TaskStatus.Done, CreatedAt = DateTime.UtcNow, CommitType = "feat",
+        });
+        await new WorktreeRepository(ctx).AddAsync(new WorktreeEntity
+        {
+            TaskId = taskId, Path = "/tmp/x", BranchName = "claudedo/x",
+            BaseCommit = "deadbeef", State = initial, CreatedAt = DateTime.UtcNow,
+        });
+        return taskId;
+    }
+
+    [Fact]
+    public async Task SetWorktreeState_Active_To_Discarded_Succeeds()
+    {
+        var taskId = await SeedWorktreeAsync(WorktreeState.Active);
+        var hub = CreateHub();
+
+        var ok = await hub.SetWorktreeState(taskId, WorktreeState.Discarded);
+
+        Assert.True(ok);
+        using var ctx = _db.CreateContext();
+        var row = await new WorktreeRepository(ctx).GetByTaskIdAsync(taskId);
+        Assert.Equal(WorktreeState.Discarded, row!.State);
+    }
+
+    [Fact]
+    public async Task SetWorktreeState_Merged_To_Active_Throws()
+    {
+        var taskId = await SeedWorktreeAsync(WorktreeState.Merged);
+        var hub = CreateHub();
+
+        await Assert.ThrowsAsync<HubException>(() =>
+            hub.SetWorktreeState(taskId, WorktreeState.Active));
+
+        using var ctx = _db.CreateContext();
+        var row = await new WorktreeRepository(ctx).GetByTaskIdAsync(taskId);
+        Assert.Equal(WorktreeState.Merged, row!.State);
+    }
+
+    [Fact]
+    public async Task SetWorktreeState_Discarded_To_Kept_Throws()
+    {
+        var taskId = await SeedWorktreeAsync(WorktreeState.Discarded);
+        var hub = CreateHub();
+
+        await Assert.ThrowsAsync<HubException>(() =>
+            hub.SetWorktreeState(taskId, WorktreeState.Kept));
+    }
+
+    [Fact]
+    public async Task SetWorktreeState_SameState_IsNoOp()
+    {
+        var taskId = await SeedWorktreeAsync(WorktreeState.Active);
+        var hub = CreateHub();
+
+        var ok = await hub.SetWorktreeState(taskId, WorktreeState.Active);
+
+        Assert.True(ok);
+    }
+
+    [Fact]
+    public async Task SetWorktreeState_Missing_Throws()
+    {
+        var hub = CreateHub();
+
+        await Assert.ThrowsAsync<HubException>(() =>
+            hub.SetWorktreeState("does-not-exist", WorktreeState.Discarded));
+    }
+}