Dock: fix double-click on title bars, centre the strip bar, close + menu

- Double-clicking a docked or floating title bar did nothing. iced keeps
  a widget's state (including the first click of a double-click) only
  while the widget tree keeps its shape, and pressing a title bar starts
  a possible drag that wrapped the workspace in an extra pointer-capture
  layer, rebuilding the title bar and forgetting the first click. The
  workspace is now always inside the same stack and mouse area; the
  capture handlers are only attached while dragging. A test drives the
  real view through iced's UserInterface (keeping its cache between
  events, as the runtime does) and fails without this fix.
- The shown group's edge bar was shorter than its row (the tooltip
  around the edge band sized it to its content), so it looked off
  centre. Band and bar now have explicit heights.
- Picking a pallet in the + menu closes the menu.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013RyGiMXcsf9HTKfqDxaQGt

src/app/view/mod.rs

@@ -1969,14 +1969,14 @@ bg={bg_ms:.1}ms n={view_count}"
         if let (Some(id), Some(target)) = (self.dock_dragging, self.dock_drag_target) {
             layers.push(self.dock_drop_preview(id, target));
         }
-        let workspace: Element<'_, Message> = if layers.len() == 1 {
-            layers.pop().expect("workspace layer")
-        } else {
-            iced::widget::Stack::with_children(layers)
-                .width(Fill)
-                .height(Fill)
-                .into()
-        };
+        // Always a stack (and, below, always a mouse area), even with nothing
+        // on top: iced keeps a widget's state only while the tree keeps its
+        // shape, and a title bar's double-click needs its first click to
+        // survive the drag that pressing the bar starts.
+        let workspace: Element<'_, Message> = iced::widget::Stack::with_children(layers)
+            .width(Fill)
+            .height(Fill)
+            .into();
         let any_dragging = self.dock_dragging.is_some();
         let any_splitting = self.dock_split_drag.is_some();
         let any_resizing = self.dock_resizing.is_some()
@@ -1984,8 +1984,10 @@ bg={bg_ms:.1}ms n={view_count}"
             || self.layer_col_dragging
             || self.xref_col_drag.is_some()
             || self.xref_split_drag;
-        let workspace: Element<'_, Message> = if any_dragging || any_resizing || any_splitting {
-            mouse_area(workspace)
+        let capturing = any_dragging || any_resizing || any_splitting;
+        let mut capture = mouse_area(workspace);
+        if capturing {
+            capture = capture
                 .on_move(move |p| Message::Dock(crate::ui::dock::DockMsg::DragMove(p)))
                 .on_release(Message::Dock(crate::ui::dock::DockMsg::DragRelease))
                 .interaction(if let Some((_, from_left)) = self.dock_float_resizing {
@@ -2000,11 +2002,9 @@ bg={bg_ms:.1}ms n={view_count}"
                     iced::mouse::Interaction::ResizingVertically
                 } else {
                     iced::mouse::Interaction::Grabbing
-                })
-                .into()
-        } else {
-            workspace
-        };
+                });
+        }
+        let workspace: Element<'_, Message> = capture.into();
         let command_line = self.command_line.view(
             allow_autocomplete,
             dyn_capturing,
@@ -2905,8 +2905,16 @@ impl OpenCADStudio {
             }
 
             // The group grip: a band on the window side holding the edge bar.
+            // Explicit heights: the tooltip around the band sizes it to its
+            // content, so a `Fill` bar would stop short of the row's bottom.
             let bar_w = if lit { 5.0 } else { 3.0 };
-            let bar = container(Space::new().width(bar_w).height(Fill)).style(move |theme: &Theme| {
+            let bar_inset = 5.0;
+            let bar = container(
+                Space::new()
+                    .width(bar_w)
+                    .height(Length::Fixed(row_h - 2.0 * bar_inset)),
+            )
+            .style(move |theme: &Theme| {
                 let palette = theme.palette();
                 let (color, glow) = if lit {
                     (Some(palette.primary.weak.color), true)
@@ -2939,13 +2947,8 @@ impl OpenCADStudio {
             let band = mouse_area(
                 container(bar)
                     .width(Length::Fixed(STRIP_GRIP_W))
-                    .height(Fill)
-                    .padding(iced::Padding {
-                        top: 5.0,
-                        bottom: 5.0,
-                        left: 0.0,
-                        right: 0.0,
-                    })
+                    .height(Length::Fixed(row_h))
+                    .align_y(iced::alignment::Vertical::Center)
                     .align_x(match side {
                         DockSide::Left => iced::alignment::Horizontal::Left,
                         DockSide::Right => iced::alignment::Horizontal::Right,
@@ -2963,7 +2966,7 @@ impl OpenCADStudio {
             .gap(4);
             let band = container(band)
                 .width(Fill)
-                .height(Fill)
+                .height(Length::Fixed(row_h))
                 .align_x(match side {
                     DockSide::Left => iced::alignment::Horizontal::Left,
                     DockSide::Right => iced::alignment::Horizontal::Right,