Re-acquire sidebar reference after clicking Rook button to avoid
stale locator capturing wrong sidebar state during transition.
PR #56 follow-up for PRI-699.
The 'Storage Classes' link is nested under the Rook sidebar button, not
at the top level. Expand the Rook section before asserting visibility.
Also uses /rook/i case-insensitive regex and waits for the plugins list
to render before searching.