fix(ui): unfreeze the operation spinner and attribute rebind churn

Three causes behind the stuck indicator:
- OperationStatus.End did not retire the generation, so tick work posted
  while the dispatcher was blocked drained afterwards and set
  ShowIndicator back to true on a finished operation.
- The startup update check ran in Task.Run; OperationStatus writes its
  observable properties on the calling thread, so the final
  ShowIndicator=false never reached the binding.
- OperationIndicator overwrote its own DataContext from the Status
  property, which re-targeted the call-site binding. It now scopes the
  DataContext to an inner panel and collapses itself when Status is
  null; every call site switched from DataContext= to Status=.

Also gates the footer connection pill in the command body instead of
CanExecute (a disabled command greyed out the ONLINE chip), and extends
OperationTiming: pid per line, 4 MB rollover, fast successes dropped
(failures always kept), and DetailsIsland.BindAsync now carries the
selection trigger via TasksIslandViewModel.SelectFrom.

src/ClaudeDo.Ui/Views/MainWindow.axaml

@@ -83,7 +83,7 @@
               <MenuItem Header="{loc:Tr shell.menu.about}" Command="{Binding OpenAboutCommand}"/>
             </MenuItem>
           </Menu>
-          <controls:OperationIndicator DataContext="{Binding UpdateCheck.Op}" Margin="8,0,0,0"/>
+          <controls:OperationIndicator Status="{Binding UpdateCheck.Op}" Margin="8,0,0,0"/>
         </StackPanel>
 
         <!-- Middle: draggable strip -->