chore(claude-do): refactor(ui): DetailsIslandViewModel (1431 Zeilen) in Sektio

Kontext: src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs ist mit 1431 Zeilen ein God-VM mit ~12 Concerns (Log-Streaming, Titel/Description-Editing, Subtasks, Child-Outcomes, Merge-Preview/-Targets, Diff, Agent-Settings-Overrides, Notes-Mode, Prep-Mode, Tabs, Session-Outcome/Roadblocks, Worktree-Info). Jedes neue Feature landet dort.

Änderungen — drei klar abgrenzbare Sektionen als ei

ClaudeDo-Task: 483e419f-1ec8-46ba-986b-8b90d6596b49

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

@@ -77,11 +77,11 @@ public class DetailsIslandConflictSeamTests : IDisposable
 
         var vm = BuildVm(new ConflictApproveWorkerClient());
         vm.Bind(new TaskRowViewModel { Id = taskId, Status = TaskStatus.WaitingForReview });
-        vm.SelectedMergeTarget = "main";
+        vm.Merge.SelectedMergeTarget = "main";
 
         string? capturedTaskId = null;
         string? capturedTarget = null;
-        vm.RequestConflictResolution = (tid, target) =>
+        vm.Merge.RequestConflictResolution = (tid, target) =>
         {
             capturedTaskId = tid;
             capturedTarget = target;