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/scene.rs

@@ -82,9 +82,10 @@ pub fn symbols(
     glyphs.draw(pos, &view, s)
 }
 
-/// Draw the model's datum planes and axes around `bounds` into `s`; returns the box around them.
-pub fn datums(s: &mut Scene, model: &fieldcraft_model::Model, bounds: &Aabb3, t: &Tokens) -> Aabb3 {
-    fieldcraft_render::glyphs::datums(model, bounds, &|_| true, &t.glyph_colors(), s)
+/// Draw the datums the session's view shows around `bounds` into `s`; returns the box around them.
+pub fn datums(s: &mut Scene, session: &fieldcraft_engine::Session, bounds: &Aabb3, t: &Tokens) -> Aabb3 {
+    let shown = |name: &str| session.shows(fieldcraft_engine::ItemKind::Datum, name);
+    fieldcraft_render::glyphs::datums(&session.model, bounds, &shown, &t.glyph_colors(), s)
 }
 
 /// The scene for `display` drawn in `style`.