Fix tree-view crash when dock pane is split

[asiloisad]

Root Cause

During startup, the tree-view item may be deserialized into a specific pane within a split dock (e.g. pane B). When activate() then calls workspace.open(treeView, ...) without searchAllPanes: true, the workspace resolves the target pane via paneContainerForURI() → container.getActivePane(), which returns the active pane in the dock (pane A), not necessarily the one holding the deserialized tree-view (pane B).

Since pane.addItem() only guards against duplicates within its own items array, the item passes the local check on pane A but fails the global ItemRegistry check — because it was already registered when deserialized into pane B.

Fix

Add searchAllPanes: true to the workspace.open call in activate(). This makes the workspace use paneForItem(item), which searches all panes across all containers, correctly locating the already-deserialized item regardless of which pane in a split dock holds it.