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/modules/draw/layers/panel.rs

@@ -1,4 +1,4 @@
-// Layers panel toggle — ribbon definition.
+// Layer Manager pallet — ribbon definition.
 
 use crate::modules::{IconKind, ModuleEvent, ToolDef};
 
@@ -7,6 +7,8 @@ pub fn tool() -> ToolDef {
         id: "LAYERS",
         label: "Layers",
         icon: IconKind::Svg(include_bytes!("../../../../assets/icons/layers/panel.svg")),
-        event: ModuleEvent::ToggleLayers,
+        // A command like the Blocks palette's: it opens the pallet, and the
+        // ribbon drops the button's highlight once it has run.
+        event: ModuleEvent::Command("LAYERS".to_string()),
     }
 }