feat(ui): list reordering, quick actions, and resizable modals

- Drag-to-reorder user lists in the sidebar, persisted via a new
  list sort_order column (AddListSortOrder migration, backfilled by
  creation time) and ListRepository.ReorderAsync
- "Open in Explorer" / "Open in Terminal" context-menu actions on lists
- "Clear all completed" button on the Tasks island
- Inline-edit subtask titles (empty text deletes the step) and
  click-to-copy task ID in the Details island
- Make modal and planning windows resizable (BorderOnly decorations
  with min sizes) instead of fixed-size borderless

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/ViewModels/Islands/ListsIslandViewModel.cs

@@ -82,6 +82,52 @@ public sealed partial class ListsIslandViewModel : ViewModelBase
         finally { _worktreesOverviewOpen = false; }
     }
 
+    [RelayCommand]
+    private void OpenInExplorer(ListNavItemViewModel? row)
+    {
+        var dir = row?.WorkingDir;
+        if (string.IsNullOrWhiteSpace(dir) || !System.IO.Directory.Exists(dir)) return;
+        try
+        {
+            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
+            {
+                FileName = dir,
+                UseShellExecute = true,
+            });
+        }
+        catch { /* best-effort */ }
+    }
+
+    [RelayCommand]
+    private void OpenInTerminal(ListNavItemViewModel? row)
+    {
+        var dir = row?.WorkingDir;
+        if (string.IsNullOrWhiteSpace(dir) || !System.IO.Directory.Exists(dir)) return;
+        try
+        {
+            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
+            {
+                FileName = "wt.exe",
+                Arguments = $"-d \"{dir}\"",
+                UseShellExecute = true,
+            });
+        }
+        catch
+        {
+            // Windows Terminal not installed — fall back to a plain console at the directory.
+            try
+            {
+                System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
+                {
+                    FileName = "cmd.exe",
+                    WorkingDirectory = dir,
+                    UseShellExecute = true,
+                });
+            }
+            catch { /* best-effort */ }
+        }
+    }
+
     public ObservableCollection<ListNavItemViewModel> Items { get; } = new();
     public ObservableCollection<ListNavItemViewModel> SmartLists { get; } = new();
     public ObservableCollection<ListNavItemViewModel> UserLists { get; } = new();
@@ -231,6 +277,57 @@ public sealed partial class ListsIslandViewModel : ViewModelBase
         }
     }
 
+    public void ClearDropHints()
+    {
+        foreach (var r in UserLists)
+        {
+            r.DropHintAbove = false;
+            r.DropHintBelow = false;
+        }
+    }
+
+    public void SetDropHint(ListNavItemViewModel target, bool placeBelow)
+    {
+        foreach (var r in UserLists)
+        {
+            var isTarget = ReferenceEquals(r, target);
+            r.DropHintAbove = isTarget && !placeBelow;
+            r.DropHintBelow = isTarget && placeBelow;
+        }
+    }
+
+    public async Task ReorderAsync(ListNavItemViewModel source, ListNavItemViewModel target, bool placeBelow)
+    {
+        if (source.Kind != ListKind.User || target.Kind != ListKind.User) return;
+        if (ReferenceEquals(source, target)) return;
+
+        MoveWithinCollection(UserLists, source, target, placeBelow);
+
+        var orderedIds = UserLists.Select(i => i.Id["user:".Length..]).ToList();
+        await using var ctx = await _dbFactory.CreateDbContextAsync();
+        var lists = new ListRepository(ctx);
+        await lists.ReorderAsync(orderedIds);
+    }
+
+    private static void MoveWithinCollection(
+        ObservableCollection<ListNavItemViewModel> coll,
+        ListNavItemViewModel source,
+        ListNavItemViewModel target,
+        bool placeBelow)
+    {
+        var srcIdx = coll.IndexOf(source);
+        var tgtIdx = coll.IndexOf(target);
+        if (srcIdx < 0 || tgtIdx < 0 || srcIdx == tgtIdx) return;
+
+        var finalIdx = placeBelow ? tgtIdx + 1 : tgtIdx;
+        if (srcIdx < finalIdx) finalIdx--;
+        if (finalIdx < 0) finalIdx = 0;
+        if (finalIdx >= coll.Count) finalIdx = coll.Count - 1;
+        if (finalIdx == srcIdx) return;
+
+        coll.Move(srcIdx, finalIdx);
+    }
+
     partial void OnSelectedListChanged(ListNavItemViewModel? value)
     {
         foreach (var i in Items) i.IsActive = ReferenceEquals(i, value);