When the user cancels a subagent tool confirmation dialog, the subagent
panel stays expanded at its pre-cancel height. This happens because
cancelConfirmation() only calls parent.layout() (relaying the turn
widget's children), but never updates the ScrolledComposite's minimum
size via refreshScrollerLayout(). On the Continue path this goes
unnoticed because subsequent subagent messages trigger a layout refresh;
on the Cancel path no further messages arrive, so the panel is stuck.

Fix by walking up the ancestor chain after parent.layout() to find the
ChatContentViewer and calling refreshScrollerLayout(), which recomputes
setMinHeight() and collapses the scroll area correctly.

Fixes microsoft#169

When the user cancels a subagent tool confirmation dialog, the subagent
panel stays expanded at its pre-cancel height. This happens because
cancelConfirmation() only called parent.layout() (relaying the turn
widget's children), but never updated the ScrolledComposite's minimum
size via refreshScrollerLayout(). On the Continue path this goes
unnoticed because subsequent subagent messages trigger a layout refresh;
on the Cancel path no further messages arrive, so the panel is stuck.

Fix by passing a Runnable callback from BaseTurnWidget into the dialog at
construction time. BaseTurnWidget walks up the ancestor chain once to
find ChatContentViewer and captures refreshScrollerLayout() as the
callback. cancelConfirmation() calls it after disposal, which recomputes
setMinHeight() in a single layout pass and collapses the panel correctly.
This also removes the redundant parent.layout() call that preceded the
deep layout(true,true) inside refreshScrollerLayout().

Fixes microsoft#169