Moved ShowDiffModal/ShowWorktreeModal delegate wiring from
AgentStripView (child, possibly detached) to DetailsIslandView
(the VM's DataContext owner). TopLevel is resolved at invocation
time, not at wiring time, so attachment order no longer matters.
AgentStripView reduced to InitializeComponent() only.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>