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/app/document.rs

@@ -797,6 +797,9 @@ impl HistorySnapshot {
                 .saturating_add(d.named_parameters.as_ref().map_or(0, |(before, after)| {
                     before.len().saturating_add(after.len()).saturating_mul(128)
                 }))
+                .saturating_add(d.visibility_states.as_ref().map_or(0, |(before, after)| {
+                    (before.len() + after.len()).saturating_mul(32)
+                }))
                 .saturating_add(d.reference_designations.len().saturating_mul(16))
                 .saturating_add(d.label.len()),
             HistorySnapshot::ObjectVisibility(v) => v
@@ -833,6 +836,11 @@ pub(super) struct ObjectVisibilitySnapshot {
 /// cloning the flat entity store.
 #[derive(Clone)]
 pub(super) struct DeltaSnapshot {
+    /// Editor current-state indices must follow undo even when two states show identical objects.
+    pub(super) visibility_states: Option<(
+        rustc_hash::FxHashMap<Handle, usize>,
+        rustc_hash::FxHashMap<Handle, usize>,
+    )>,
     pub(super) entities: Vec<(Handle, Option<Arc<EntityType>>, Option<Arc<EntityType>>)>,
     pub(super) current_layout_before: String,
     pub(super) current_layout_after: String,
@@ -949,6 +957,7 @@ pub(super) struct HistoryState {
 }
 
 pub(super) struct PendingHistorySnapshot {
+    pub(super) visibility_states_before: rustc_hash::FxHashMap<Handle, usize>,
     pub(super) label: String,
     pub(super) current_layout: String,
     pub(super) active_layer: String,