fix(shell): let the folder tree grow instead of scrolling internally

A bound prefHeight is only ever a request — TreeView's own max height
stayed unconstrained, so an ancestor giving it less room than that let
its internal ScrollBar pick up the difference instead of the tree
actually growing. Pinning min/max to USE_PREF_SIZE forces it to grow,
so NavigationSidebar's own outer ScrollPane is the only one that scrolls.

src/main/java/org/icroco/pholio/ui/shell/LibraryFolderTree.java

@@ -143,6 +143,13 @@ public class LibraryFolderTree extends StackPane implements Disposable {
         // already tracks branch expand/collapse and root add/remove alike, so this needs no separate
         // listener of its own.
         tree.prefHeightProperty().bind(tree.expandedItemCountProperty().multiply(32).add(2));
+        // A bound prefHeight alone is only ever a request — TreeView's own default max height stays
+        // unconstrained, but nothing stops an ancestor from giving it less than that and letting its own
+        // internal ScrollBar pick up the difference instead. Pinning min/max to it is what actually forces
+        // the tree to grow (never scroll internally): NavigationSidebar's own outer ScrollPane, wrapped
+        // around the whole destination list, is meant to be the only one that ever does.
+        tree.setMinHeight(Region.USE_PREF_SIZE);
+        tree.setMaxHeight(Region.USE_PREF_SIZE);
         // The tree fills the drawer, which already has its own border; EDGE_TO_EDGE drops the control's
         // so the two do not stack into a double line.
         tree.getStyleClass().add(Tweaks.EDGE_TO_EDGE);