perf(statusbar): cache layout/scale derived data behind epochs (major)

Status bar rescanned the whole object map twice per frame (layout_names +
scale_picker_list), deep-cloned an already-cached Arc, and built two
undo/redo label vecs consumed ~never. Cache layout names (epoch key) and
scale picker (epoch + unit-factor + imperial-family + current-scale key)
as Arc behind choke-point invalidation (layout/scale impl methods,
undo/redo swaps, file-open, doc-reset); borrow across the widget boundary
(owned-Arc params; E0515 forbids &'a slices over call-site temporaries);
build undo/redo labels only when their dropdown is open.

Tests:
- cached_layout_names_returns_same_arc_until_bump: hit-path Arc identity
- cached_layout_names_invalidated_by_add_layout: bump yields new Arc + names
- cached_scale_picker_returns_same_arc_until_bump: hit-path Arc identity
- cached_scale_picker_invalidated_by_add_scale: bump yields new Arc + scale
- cached_scale_picker_invalidated_by_current_scale_change: key completeness

Bench (cargo bench ui_statusbar_derived_data, 3k entities): cached hit below
timer granularity vs ~1us uncached scans, PASS (50us threshold).

src/ui/popup/scale_popup.rs

@@ -17,11 +17,12 @@ pub fn menu_entries(
     is_model: bool,
     current_scale_name: &str,
     viewport_scale: Option<f64>,
-    file_scales: Vec<(String, f32, f64)>,
+    file_scales: &[(String, f32, f64)],
 ) -> Vec<Entry<'static>> {
     let mut entries: Vec<Entry<'static>> = file_scales
-        .into_iter()
+        .iter()
         .map(|(label, _anno_scale, vp_scale)| {
+            let vp_scale = *vp_scale;
             let active = if is_model {
                 label.eq_ignore_ascii_case(current_scale_name)
             } else {
@@ -38,7 +39,7 @@ pub fn menu_entries(
             } else {
                 Message::SetViewportScale(label.clone())
             };
-            Entry::close(scale_row(label, active, msg))
+            Entry::close(scale_row(label.clone(), active, msg))
         })
         .collect();
 

src/ui/popup/selection_filter_popup.rs

@@ -14,7 +14,7 @@ use crate::ui::statusbar::status_menu::Entry;
 /// - `types`: entity-type names present in the current layout.
 /// - `excluded`: types currently filtered out (unchecked).
 pub fn menu_entries(
-    types: Vec<String>,
+    types: &[String],
     excluded: &HashSet<String>,
 ) -> Vec<Entry<'static>> {
     // "Select All / Clear All" header, mirroring the OSNAP popup: Select All
@@ -51,10 +51,10 @@ pub fn menu_entries(
         vec![Entry::stay(empty_row())]
     } else {
         types
-            .into_iter()
+            .iter()
             .map(|name| {
-                let included = !excluded.contains(&name);
-                Entry::stay(type_row(name, included))
+                let included = !excluded.contains(name);
+                Entry::stay(type_row(name.clone(), included))
             })
             .collect()
     };