Dock: simplify drag, peek, width and open/close state

No intended behaviour change except the fixes noted below.

- One drag state: a single `DockDrag` (move pallet / group, width,
  splitter, floating size, Layer Manager column) replaces nine fields
  (dragging, dragging group, resizing, split, float resizing, origin,
  target, grab offset, layer column flag) that had to be kept in sync.
- `dock_expanded` becomes `dock_peek` with one meaning: a pallet revealed
  although it auto-hides. `dock_reveal(id)` shows a pallet's group and
  peeks it; commands that open a pallet now use it, so opening a pallet
  also switches its edge to that pallet's group.
- Each group stores its own width (falling back to its widest pallet's
  width until first sized), instead of every pallet's width being kept in
  sync. Pallet widths now only size floating pallets and new groups.
- One `dock_set_open(id, open)` holds every pallet's open and close path.
- Leftovers removed: the tab-group config format that never reached main,
  the multi-tab drag ghost header, the separate icon-hover message.

Fixes:
- Hovering a strip icon reveals an auto-hiding edge again (the icons had
  lost the hover message in the option B strip). Covered by a test that
  moves the pointer over the icon in the real view.

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

src/app/mod.rs

@@ -845,41 +845,23 @@ pub(super) struct OpenCADStudio {
     pub(crate) bg_picker: Option<BgTarget>,
     /// General edge-stack dock layout for the side panels.
     pub(crate) dock: crate::ui::dock::DockState,
-    /// Which panel is currently floated at full height (hovered, or a pinned
-    /// panel on top).
-    pub(crate) dock_expanded: Option<crate::ui::dock::PanelId>,
-    /// Panel currently being dragged between sides / reordered.
-    pub(crate) dock_dragging: Option<crate::ui::dock::PanelId>,
-    /// Panel currently being width-resized.
-    pub(crate) dock_resizing: Option<crate::ui::dock::PanelId>,
-    /// Last pointer position during a drag / resize.
+    /// Pallet revealed although it auto-hides (its edge's group, or its
+    /// floating frame): hovered, being dragged, or just opened. Cleared when
+    /// the pointer leaves.
+    pub(crate) dock_peek: Option<crate::ui::dock::PanelId>,
+    /// 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>,
+    /// Pallet whose strip icon (or floating frame) the pointer is over.
+    pub(crate) dock_icon_hover: Option<crate::ui::dock::PanelId>,
+    /// Last pointer position during a dock drag.
     pub(crate) dock_drag_last: Option<iced::Point>,
-    /// Live drop target, shown as a preview while dragging. `None` until the
-    /// pointer has moved far enough to count as a drag, so a click on a title
-    /// bar or tab never moves the panel.
-    pub(crate) dock_drag_target: Option<crate::ui::dock::DropTarget>,
-    /// First pointer position of the current panel drag.
-    pub(crate) dock_drag_origin: Option<iced::Point>,
-    /// Pointer offset from a dragged panel's top-left corner, so a floated
-    /// panel lands where it is held rather than jumping to the pointer.
-    pub(crate) dock_grab_offset: iced::Vector,
-    /// Splitter being dragged between two pallets of a group (side, group,
-    /// upper, lower).
-    pub(crate) dock_split_drag: Option<(crate::app::config::DockSide, usize, usize, usize)>,
-    /// Floating panel being resized from its corner grip, and whether from
-    /// the bottom-left corner.
-    pub(crate) dock_float_resizing: Option<(crate::ui::dock::PanelId, bool)>,
     /// Docked panel whose title bar the pointer is over (shows pin / close).
     pub(crate) dock_title_hover: Option<crate::ui::dock::PanelId>,
     /// Edge whose icon-strip pallet menu (+) is open.
     pub(crate) dock_edge_menu: Option<crate::app::config::DockSide>,
-    /// Group being dragged by its strip grip (side, slot index). While set,
-    /// `dock_dragging` holds the group's shown panel for the preview.
-    pub(crate) dock_dragging_group: Option<(crate::app::config::DockSide, usize)>,
     /// Group whose edge band (group grip) the pointer is over.
     pub(crate) dock_grip_hover: Option<(crate::app::config::DockSide, usize)>,
-    /// Pallet whose strip icon the pointer is over.
-    pub(crate) dock_icon_hover: Option<crate::ui::dock::PanelId>,
     /// Reference-table column currently being width-resized (column index),
     /// with the last pointer position. Mirrors the Layers Name-column drag.
     pub(crate) xref_col_drag: Option<usize>,
@@ -968,9 +950,6 @@ pub(super) struct OpenCADStudio {
     modal_drag_last: Option<Point>,
     /// True while the modal title bar is held (a drag is in progress).
     modal_dragging: bool,
-    /// Layer Manager: dragging the Name-column divider (width follows the
-    /// shared ModalDragMove flow).
-    layer_col_dragging: bool,
     /// Layer Manager Name column width in px, adjusted by the divider drag.
     layer_name_col_w: f32,
     /// How far the user has dragged the modal's corner resize grip from the
@@ -4310,18 +4289,11 @@ impl OpenCADStudio {
             block_palette: Default::default(),
             xref_manager: Default::default(),
             dock: Default::default(),
-            dock_expanded: None,
-            dock_dragging: None,
-            dock_resizing: None,
+            dock_peek: None,
+            dock_drag: None,
             dock_drag_last: None,
-            dock_drag_target: None,
-            dock_drag_origin: None,
-            dock_grab_offset: iced::Vector::new(0.0, 0.0),
-            dock_split_drag: None,
-            dock_float_resizing: None,
             dock_title_hover: None,
             dock_edge_menu: None,
-            dock_dragging_group: None,
             dock_grip_hover: None,
             dock_icon_hover: None,
             xref_col_drag: None,
@@ -4360,7 +4332,6 @@ impl OpenCADStudio {
             modal_offset: iced::Vector::ZERO,
             modal_drag_last: None,
             modal_dragging: false,
-            layer_col_dragging: false,
             layer_name_col_w: 130.0,
             modal_resize: iced::Vector::ZERO,
             modal_content_size: None,