R5.6: ElyShow right-click menus, PowerPoint-style; Impress table borders drag; R3 PASS

The canvas offers Ely's menu by target: slide (layouts, comment), text
(bullets, numbering, comment), shape or text box, picture (replace,
crop), table (insert, delete, merge), each item gated by the kernel's
state for its own command. Impress's table borders read as text and
drag through R5.3's path; patch 0047 reports every edge's bounds and
makes the left edge drag. A line past its bound never moves against
the drag, so a still press sends nothing.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/ely-show/src/deck.rs

@@ -57,6 +57,8 @@ pub struct Deck {
     pub remarks_pane: Entity<crate::remarks::Pane>,
     /// What the menus last checked: grid, guides, comments.
     pub snap_menus: Option<(bool, bool, bool)>,
+    /// The canvas's right-click menu.
+    pub menu: Option<ely_office::menu::Offer<crate::menu::What>>,
     /// Pictures of closed tabs and ended previews, freed later.
     pub retired: ely_gpui_component::primitives::Retired,
 }
@@ -103,6 +105,7 @@ impl Host for Deck {
             tab.extra.dark = dark;
             self.repaint_all(id, cx);
         }
+        self.offer_menu(id, view, cx);
         self.reread(id, view, cx);
     }
 }
@@ -172,6 +175,7 @@ impl Deck {
             reading_fonts: false,
             guide_drag: None,
             snap_menus: Some((false, false, false)),
+            menu: None,
             notes: Default::default(),
             remarks_open: false,
             preview: None,
@@ -379,7 +383,7 @@ impl Deck {
         self.paint_next(id, cx);
     }
 
-    fn body(&mut self, window: &mut Window, cx: &mut Context<Self>) -> AnyElement {
+    pub(crate) fn body(&mut self, window: &mut Window, cx: &mut Context<Self>) -> AnyElement {
         let Some(tab) = self.active_tab() else {
             let title = match self.core.loading.first() {
                 Some((_, name)) => Self::text(cx, "office.loading", &[("name", name)]),
@@ -447,7 +451,8 @@ impl Render for Deck {
             .on_action(cx.listener(Self::on_close_tab))
             .child(shell)
             .children(self.core_dialog(cx))
-            .children(self.dialog_element(cx));
+            .children(self.dialog_element(cx))
+            .children(self.context_menu(cx));
         let root = crate::slideshow::bind(crate::insert::bind(crate::slides::bind(root, cx), cx), cx);
         Self::bind_zoom(root, cx)
     }