feat(statusbar): selection filtering by object type (FILTER pill)

Add a per-type selection filter to the scene: the FILTER pill opens a
checklist of the entity types in the layout, and unchecking a type
excludes it from interactive picking (click, box and lasso selection all
honour it). The pill lights up while any type is filtered out.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/statusbar.rs

@@ -65,6 +65,8 @@ impl StatusBar {
         transparency_display: bool,
         // Whether the Quick Properties floating panel is enabled.
         quick_properties: bool,
+        // True when the selection filter is excluding at least one type.
+        selection_filter_active: bool,
         // Which pills the user has chosen to show on the bar.
         config: &'a StatusBarConfig,
     ) -> Element<'a, Message> {
@@ -201,6 +203,16 @@ impl StatusBar {
                 "Quick Properties\nFloating panel on selection",
             ));
         }
+        if vis(StatusPill::SelFilter) {
+            right_status = right_status.push(tip(
+                toggle_pill(
+                    "FILTER",
+                    selection_filter_active,
+                    Message::ToggleSelectionFilterPopup,
+                ),
+                "Selection Filtering\nLimit which object types can be picked",
+            ));
+        }
         if vis(StatusPill::Vp) && !vp_label.is_empty() {
             right_status = right_status.push(tip(
                 status_pill(vp_label).into(),