feat(ui): add dockable properties panel

Preserve panel width across left/right docking and persist resize, position, and auto-collapse preferences.

Refs #348
Refs #650

src/app/update/file.rs

@@ -520,6 +520,11 @@ impl OpenCADStudio {
                 section: self.start_section,
             },
             statusbar: self.statusbar_config.clone(),
+            properties: crate::app::config::PropertiesDockConfig {
+                side: self.properties_side,
+                width: self.properties_width,
+                auto_collapse: self.properties_auto_collapse,
+            },
             annotation_auto_scale: self.annotation_auto_scale,
             ribbon: crate::app::config::RibbonConfig {
                 collapse: self.ribbon.collapse_mode(),
@@ -550,6 +555,13 @@ impl OpenCADStudio {
         // (`refresh_recent_thumbs`) — never here on the boot path.
         self.start_section = cfg.start.section;
         self.statusbar_config = cfg.statusbar;
+        self.properties_side = cfg.properties.side;
+        self.properties_width = if cfg.properties.width.is_finite() {
+            cfg.properties.width.clamp(220.0, 600.0)
+        } else {
+            250.0
+        };
+        self.properties_auto_collapse = cfg.properties.auto_collapse;
         self.annotation_auto_scale = cfg.annotation_auto_scale.clamp(-4, 4);
         self.ribbon.set_collapse_mode(cfg.ribbon.collapse);
         self.plot_dialog = cfg.plot;

src/app/update/mod.rs

@@ -350,6 +350,110 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::PropertiesClose => {
+                self.show_properties = false;
+                self.properties_hovered = false;
+                self.properties_dragging = false;
+                self.properties_resizing = false;
+                self.properties_drag_last = None;
+                self.properties_dock_preview = None;
+                self.ribbon.set_properties(false);
+                Task::none()
+            }
+
+            Message::PropertiesAutoCollapseToggle => {
+                self.properties_auto_collapse ^= true;
+                // Keep the panel open while the pointer is still over the
+                // button; leaving the panel performs the first collapse.
+                self.properties_hovered = self.properties_auto_collapse;
+                self.save_config();
+                Task::none()
+            }
+
+            Message::PropertiesHover(hovered) => {
+                if self.properties_auto_collapse
+                    && !self.properties_dragging
+                    && !self.properties_resizing
+                {
+                    self.properties_hovered = hovered;
+                }
+                Task::none()
+            }
+
+            Message::PropertiesDockGrab => {
+                self.properties_dragging = true;
+                self.properties_resizing = false;
+                self.properties_drag_last = None;
+                self.properties_dock_preview = Some(self.properties_side);
+                self.properties_hovered = true;
+                Task::none()
+            }
+
+            Message::PropertiesResizeGrab => {
+                self.properties_resizing = true;
+                self.properties_dragging = false;
+                self.properties_drag_last = None;
+                self.properties_dock_preview = None;
+                self.properties_hovered = true;
+                Task::none()
+            }
+
+            Message::PropertiesWidthReset => {
+                self.properties_width = 250.0;
+                self.save_config();
+                Task::none()
+            }
+
+            Message::PropertiesDragMove(point) => {
+                if self.properties_dragging {
+                    self.properties_dock_preview = Some(if point.x < self.win_size.0 * 0.5 {
+                        crate::app::config::DockSide::Left
+                    } else {
+                        crate::app::config::DockSide::Right
+                    });
+                } else if self.properties_resizing {
+                    if let Some(last) = self.properties_drag_last {
+                        let dx = point.x - last.x;
+                        let delta = match self.properties_side {
+                            crate::app::config::DockSide::Left => dx,
+                            crate::app::config::DockSide::Right => -dx,
+                        };
+                        let max_width = (self.win_size.0 * 0.45).clamp(220.0, 600.0);
+                        self.properties_width =
+                            (self.properties_width + delta).clamp(220.0, max_width);
+                    }
+                }
+                if self.properties_dragging || self.properties_resizing {
+                    self.properties_drag_last = Some(point);
+                }
+                Task::none()
+            }
+
+            Message::PropertiesDragRelease => {
+                let changed = if self.properties_dragging {
+                    if let Some(side) = self.properties_dock_preview {
+                        let changed = side != self.properties_side;
+                        self.properties_side = side;
+                        changed
+                    } else {
+                        false
+                    }
+                } else {
+                    self.properties_resizing
+                };
+                self.properties_dragging = false;
+                self.properties_resizing = false;
+                self.properties_drag_last = None;
+                self.properties_dock_preview = None;
+                if self.properties_auto_collapse {
+                    self.properties_hovered = false;
+                }
+                if changed {
+                    self.save_config();
+                }
+                Task::none()
+            }
+
             Message::ScrollLayoutTabs(dx) => iced::widget::operation::scroll_by(
                 iced::advanced::widget::Id::new(crate::ui::statusbar::LAYOUT_TABS_SCROLL_ID),
                 iced::widget::scrollable::AbsoluteOffset { x: dx, y: 0.0 },