Dock: LAYERS opens its pallet like Insert Block, Layer Manager layout fixes, 150 ms auto-hide hover delay

- LAYERS ribbon button runs a command that opens the Layer Manager pallet;
  the ribbon no longer keeps it highlighted.
- Layer Manager: search box stays right-aligned, the column header fills
  the row, no stray contour lines when the pallet is taller than its rows.
- Auto-hidden edges don't show the shown-group accent bar.
- Auto-hide reveal and hide wait 150 ms of rest, so passing over the
  strip doesn't flash groups open.

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

src/app/mod.rs

@@ -850,6 +850,10 @@ pub(super) struct OpenCADStudio {
     /// floating frame): hovered, being dragged, or just opened. Cleared when
     /// the pointer leaves.
     pub(crate) dock_peek: Option<crate::ui::dock::PanelId>,
+    /// Reveal (`Some(pallet)`) or hide (`None`) waiting out the hover delay,
+    /// with the generation its timer carries; any newer hover supersedes it.
+    pub(crate) dock_hover_pending: Option<Option<crate::ui::dock::PanelId>>,
+    pub(crate) dock_hover_gen: u64,
     /// What the pointer is dragging in the dock (pallet, group, width,
     /// splitter, floating size, Layer Manager column).
     pub(crate) dock_drag: Option<crate::ui::dock::DockDrag>,
@@ -4291,6 +4295,8 @@ impl OpenCADStudio {
             xref_manager: Default::default(),
             dock: Default::default(),
             dock_peek: None,
+            dock_hover_pending: None,
+            dock_hover_gen: 0,
             dock_drag: None,
             dock_drag_last: None,
             dock_title_hover: None,