Feat: Phase 1.5 — viewport count in status bar + REVCLOUD command

Status bar: shows "N VP" pill (with tooltip) when in a paper layout that has
user viewports (id > 1). New Scene::viewport_count() method.

REVCLOUD: closed LwPolyline with arc bumps (bulge = 0.5) along each edge.
Click polygon corners, Enter to close into a revision cloud shape.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/app/view.rs

@@ -166,6 +166,7 @@ impl H7CAD {
                     tab.scene.current_layout.clone(),
                     self.layout_rename_state.as_ref(),
                     tab.scene.first_viewport_scale(),
+                    tab.scene.viewport_count(),
                 )
             ]
             .width(Fill)