Browser and viewport: item menu, per-item eyes, Delete key with confirmation

Right-click on any browser item (body, surface, datum, partition, set,
material, section, step, boundary condition, load, reference point,
coupling, contact, fluid domain) opens its menu: Edit…, Hide/Show,
Isolate, Show All, Active in step (boundary conditions and loads) and
Delete…. A right click on a datum or a partition's cut face in the
viewport opens the same menu. Each item the viewport draws on its own
has an eye; hidden items are neither drawn nor picked. Datums and
partitions are selectable with properties. Delete… and the Delete key
ask first (the prompt lists what uses the item: a datum's partitions
are deleted with it, other definitions in use are refused); ui.prompt
answers it. Every entry runs the same command as the ribbon and forms.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/files.rs

@@ -272,6 +272,9 @@ pub enum Prompt {
     /// A design (its path) has none of the bodies the model's mesh and sets are on: start a new
     /// model with it, or keep the model. The opened session waits in [`ModelApp::held`].
     Design(String),
+    /// Delete a definition (the item menu's Delete…, the Delete key): what uses it is listed, and
+    /// the deletion refused or (a datum's partitions) done with it.
+    Delete(crate::menu::DeleteAsk),
 }
 
 /// The answer to [`Prompt::Design`].
@@ -871,6 +874,32 @@ pub fn show(app: &mut ModelApp, ctx: &egui::Context) {
                 app.answer_design(a);
             }
         }
+        Some(Prompt::Delete(ask)) => {
+            let mut answer = None;
+            crate::frame::window(ctx, "Delete", crate::frame::Width::Normal).id(egui::Id::new("fc_delete")).show(ctx, |ui| {
+                ui.label(ask.question());
+                if ask.allowed() && !ask.users.is_empty() {
+                    ui.label(egui::RichText::new("They are deleted too; Undo brings everything back.").color(t.text_dim));
+                }
+                ui.add_space(6.0);
+                ui.horizontal(|ui| {
+                    if ask.allowed() && ui.button("Delete").clicked() {
+                        answer = Some(true);
+                    }
+                    if ui.button(if ask.allowed() { "Cancel" } else { "Close" }).clicked() {
+                        answer = Some(false);
+                    }
+                });
+            });
+            if ctx.input(|i| i.key_pressed(egui::Key::Escape)) {
+                answer = Some(false);
+            } else if ctx.input(|i| i.key_pressed(egui::Key::Enter)) {
+                answer = Some(ask.allowed());
+            }
+            if let Some(delete) = answer {
+                app.answer_delete(delete);
+            }
+        }
         Some(Prompt::ReplaceMesh(r)) => {
             let mut answer = None;
             crate::frame::window(ctx, "Replace mesh", crate::frame::Width::Normal).id(egui::Id::new("fc_replace_mesh")).show(ctx, |ui| {