feat(block-editor): add functional Visibility ribbon controls

Add the current-state selector, Visibility States dialog and mode/show/hide
controls to the contextual ribbon, using shared icons, tooltips, modal UI
and adaptive flyouts. Disable the controls until a Visibility parameter exists.

Stage state creation, rename, deletion, current-state changes and reordering
until OK. Support copied, show-all and hide-all new states in one undo step,
preserve native graph metadata, and restore current-state identity on undo/redo.

Implement nonsaved BVMODE and display-only reveal during BVSHOW selection.
Cancelling selection leaves saved visibility flags and history unchanged.
Keep the existing command-line state workflows available.

Validation: 6 targeted tests; 277 block, 31 app dock, 35 ribbon and 12 history
checks passed (overlapping filters). All 17 local DWG fixtures passed in-memory
DWG/DXF preservation checks with unchanged original checksums.

src/command.rs

@@ -2991,6 +2991,12 @@ pub trait CadCommand: Send {
     /// While true, viewport clicks are routed through the normal selection
     /// system (single / box / polygon) instead of the command's point-pick path.
     /// After each completed selection action the host calls `on_selection_complete`.
+    /// A selection command may reveal state-hidden BEDIT members for picking.
+    /// This is a display request only; the document visibility flags stay intact.
+    fn reveals_hidden_block_objects(&self) -> bool {
+        false
+    }
+
     fn is_selection_gathering(&self) -> bool {
         false
     }