feat(ui): Mission Control Recent Sessions mit verschachtelten Handoffs

Neue Tabelle mission_control_sessions (Migration AddMissionControlSessions), befuellt vom
InteractiveLaunchSpecService bei Task-, Ad-hoc- und Handoff-Kacheln. Flyout im Mission-Control-Header
listet die letzten 14 Tage / 50 Sessions, Handoffs eingerueckt unter ihrer Ursprungs-Session, mit
Fortsetzen (--resume im gespeicherten cwd) und Brief anzeigen.

tests/ClaudeDo.Ui.Tests/ViewModels/MissionControlViewModelTests.cs

@@ -42,6 +42,23 @@ public class MissionControlViewModelTests : IDisposable
     private MissionControlViewModel BuildVm(StubWorkerClient worker)
         => new MissionControlViewModel(new TestDbFactory(NewContext), worker, new UsagePillViewModel(worker));
 
+    [Fact]
+    public void RecentSessions_NestHandoffs_PutsIndirectHandoffsUnderTheirOrigin()
+    {
+        var t0 = new DateTime(2026, 9, 28, 8, 0, 0, DateTimeKind.Utc);
+        MissionControlSessionEntity S(string id, int minutes, string? from = null)
+            => new() { SessionId = id, Cwd = "c", Title = id, StartedAt = t0.AddMinutes(minutes), PredecessorSessionId = from };
+        // Newest first, as ListRecentAsync returns them. "orphan" names a predecessor outside the window.
+        var newestFirst = new[] { S("c", 40, "b"), S("other", 30), S("b", 20, "a"), S("orphan", 15, "gone"), S("a", 10) };
+
+        var rows = MissionControlViewModel.NestHandoffs(newestFirst)
+            .Select(r => (r.Session.SessionId, r.IsHandoff)).ToList();
+
+        Assert.Equal(
+            new[] { ("a", false), ("b", true), ("c", true), ("other", false), ("orphan", false) },
+            rows);
+    }
+
     // Gates the title/list-name DB lookup behind a manually-released TaskCompletionSource so two
     // overlapping Open*ConPtySessionAsync calls both run their synchronous dedupe-check prefix
     // to completion before either resumes past the DB await. This reproduces the open-path races