Dock: floating menu at the pointer, hover-only bar buttons, Allow docking, clip pallets

- The floating title bar's right-click menu opens where the pointer is,
  flipped to stay on screen; the Pallets submenu sits beside it.
- Close and pin on a floating title bar only show while it is hovered,
  as on docked title bars.
- New Allow docking check in that menu: off, dragging the window (or a
  pallet out of it) only floats it, never docks it on an edge.
- Floating windows and stacked pallets clip their content, so a pallet
  sized below its content no longer draws outside its frame.

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

src/app/dock/tests.rs

@@ -628,3 +628,20 @@ fn blockpalette_width_reset() {
     let _ = app.on_dock(crate::ui::dock::DockMsg::WidthReset(id));
     assert_eq!(app.dock.group_width(DockSide::Right, 0), 260.0);
 }
+
+#[test]
+fn a_window_without_allow_docking_only_floats_when_dragged() {
+    use crate::ui::dock::{DockMsg, DropTarget, PanelId};
+    let mut app = dock_app();
+    let _ = app.on_dock(DockMsg::FloatOut(PanelId::BlockPalette));
+    let _ = app.on_dock(DockMsg::FloatDockingToggle(PanelId::BlockPalette));
+    assert!(!app.dock.float_rect(PanelId::BlockPalette).unwrap().docking);
+    // Dragged onto the left edge's strip, it stays a floating window.
+    let _ = app.on_dock(DockMsg::FloatGrab(PanelId::BlockPalette));
+    let _ = app.on_dock(DockMsg::DragMove(iced::Point::new(500.0, 300.0)));
+    let _ = app.on_dock(DockMsg::DragMove(iced::Point::new(10.0, 60.0)));
+    assert!(matches!(drag_target(&app), Some(DropTarget::Float { .. })));
+    let _ = app.on_dock(DockMsg::DragRelease);
+    assert!(app.dock.float_rect(PanelId::BlockPalette).is_some());
+    assert_eq!(app.dock.location(PanelId::BlockPalette), None);
+}