feat(ui): modernize DSETTINGS dialog with tabbed layout and action controls

- Redesign drafting settings window to landscape 700x480 proportions while preserving interactive resizing
- Add 7-tab navigation: Snap and Grid, Polar Tracking, Object Snap, 3D Object Snap, Dynamic Input, Quick Properties, and Selection Cycling
- Distribute existing drafting modes, snap options, and isometric tools into their respective tabs
- Implement OK, Apply, and Close action buttons with unsaved changes confirmation guard

src/app/drafting_settings.rs

@@ -0,0 +1,170 @@
+use super::OpenCADStudio;
+use crate::ui::window::drafting_settings::{DraftingSettingsState, DraftingSettingsTab};
+
+impl DraftingSettingsState {
+    pub(crate) fn from_app(app: &OpenCADStudio) -> Self {
+        Self {
+            active_tab: DraftingSettingsTab::SnapAndGrid,
+            snap_on: app.snapper.grid_snap(),
+            grid_on: app.show_grid,
+            isometric: app.isometric_drafting,
+            iso_plane: app.iso_plane,
+            snap_angle_deg: app.snap_angle_deg,
+            polar_on: app.polar_mode,
+            ortho_on: app.ortho_mode,
+            polar_increment_deg: app.polar_increment_deg,
+            osnap_on: app.snapper.snap_enabled,
+            otrack_on: app.snapper.otrack_enabled,
+            snap_modes: app.snapper.enabled.clone(),
+            osnap3d_on: false,
+            dyn_input_on: app.dyn_input,
+            quick_props_on: app.quick_properties,
+            selection_cycling_on: app.selection_cycling,
+        }
+    }
+}
+
+impl OpenCADStudio {
+    pub(super) fn drafting_settings_dirty(&self) -> bool {
+        match (&self.drafting_settings_state, &self.drafting_settings_saved) {
+            (Some(curr), Some(saved)) => curr.is_dirty(saved),
+            (Some(_), None) => true,
+            _ => false,
+        }
+    }
+
+    pub(super) fn apply_drafting_settings(&mut self) {
+        if let Some(state) = &self.drafting_settings_state {
+            self.show_grid = state.grid_on;
+            self.snapper.grid_snap_on = state.snap_on;
+            self.isometric_drafting = state.isometric;
+            self.iso_plane = state.iso_plane;
+            self.snap_angle_deg = state.snap_angle_deg;
+            self.polar_mode = state.polar_on;
+            self.ortho_mode = state.ortho_on;
+            self.polar_increment_deg = state.polar_increment_deg;
+            self.snapper.snap_enabled = state.osnap_on;
+            self.snapper.otrack_enabled = state.otrack_on;
+            self.snapper.enabled = state.snap_modes.clone();
+            self.dyn_input = state.dyn_input_on;
+            self.quick_properties = state.quick_props_on;
+            self.selection_cycling = state.selection_cycling_on;
+            self.sync_vport_display(self.active_tab);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_drafting_settings_tab_switching_not_dirty() {
+        let state1 = DraftingSettingsState {
+            active_tab: DraftingSettingsTab::SnapAndGrid,
+            snap_on: false,
+            grid_on: true,
+            isometric: false,
+            iso_plane: crate::app::settings::IsoPlane::Left,
+            snap_angle_deg: 0.0,
+            polar_on: false,
+            ortho_on: false,
+            polar_increment_deg: 15.0,
+            osnap_on: true,
+            otrack_on: false,
+            snap_modes: rustc_hash::FxHashSet::default(),
+            osnap3d_on: false,
+            dyn_input_on: false,
+            quick_props_on: false,
+            selection_cycling_on: false,
+        };
+        let mut state2 = state1.clone();
+        assert!(!state2.is_dirty(&state1));
+
+        // Switching tabs should NOT mark it dirty
+        state2.active_tab = DraftingSettingsTab::ObjectSnap;
+        assert!(!state2.is_dirty(&state1));
+
+        // Toggling a setting should mark it dirty
+        state2.grid_on = false;
+        assert!(state2.is_dirty(&state1));
+    }
+
+    #[test]
+    fn test_drafting_settings_dirty_toggles() {
+        let base = DraftingSettingsState {
+            active_tab: DraftingSettingsTab::SnapAndGrid,
+            snap_on: false,
+            grid_on: true,
+            isometric: false,
+            iso_plane: crate::app::settings::IsoPlane::Left,
+            snap_angle_deg: 0.0,
+            polar_on: false,
+            ortho_on: false,
+            polar_increment_deg: 15.0,
+            osnap_on: true,
+            otrack_on: false,
+            snap_modes: rustc_hash::FxHashSet::default(),
+            osnap3d_on: false,
+            dyn_input_on: false,
+            quick_props_on: false,
+            selection_cycling_on: false,
+        };
+
+        let mut modded = base.clone();
+        modded.snap_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.isometric = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.iso_plane = crate::app::settings::IsoPlane::Top;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.snap_angle_deg = 45.0;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.polar_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.ortho_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.polar_increment_deg = 30.0;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.osnap_on = false;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.otrack_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.snap_modes.insert(crate::snap::SnapType::Endpoint);
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.osnap3d_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.dyn_input_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.quick_props_on = true;
+        assert!(modded.is_dirty(&base));
+
+        let mut modded = base.clone();
+        modded.selection_cycling_on = true;
+        assert!(modded.is_dirty(&base));
+    }
+}