feat(plot): unified plot/print dialog, retire Page Setup

Replace the old Page Setup panel with a single OCS-styled plot/print
dialog (dropdowns for printer, paper, orientation, rotation, plot area,
scale, quality, shaded plot; checkboxes for plot options). PLOT / PRINT
/ PAGESETUP all open it.

- Printer output via lp: -d printer, -n copies, -o ColorModel=Gray,
  print-quality, Resolution; Windows printto verb; list_printers via
  lpstat. Preview opens a temp PDF in the OS viewer (never a save
  dialog). PDF export reuses the tested pipeline.
- Window pick returns to the new dialog (was the old Page Setup) and the
  clipped window plot drives PDF / printer / preview.
- Remember the user's print preferences across sessions in
  config/plot.txt (printer, copies, quality, output options, area,
  scale); drawing-specific fields (offset/center/rotation) seed from the
  layout. Default plot area Window, scale Fit.
- Delete src/ui/window/page_setup.rs and its ModalKind / Message /
  buffer state; fold on_page_setup_commit into apply_plot_page_settings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/view/mod.rs

@@ -1466,7 +1466,7 @@ impl OpenCADStudio {
             PluginManager => (520, 460),
             UpdateNotice => (560, 460),
             Layers => (900, 360),
-            PageSetup => (520, 460),
+            Plot => (660, 540),
             LayoutManager => (640, 320),
             Plotstyle => (780, 540),
             TextStyle => (860, 480),

src/app/view/modal.rs

@@ -47,22 +47,9 @@ impl OpenCADStudio {
                 let tab = &self.tabs[self.active_tab];
                 sized(tab.layers.view_window(), 900, 360)
             }
-            super::super::ModalKind::PageSetup => sized(
-                crate::ui::window::page_setup::view_window(
-                    &self.page_setup_w,
-                    &self.page_setup_h,
-                    &self.page_setup_plot_area,
-                    self.page_setup_center,
-                    &self.page_setup_offset_x,
-                    &self.page_setup_offset_y,
-                    &self.page_setup_rotation,
-                    &self.page_setup_scale,
-                    self.plot_format,
-                    self.plot_orientation,
-                ),
-                520,
-                460,
-            ),
+            super::super::ModalKind::Plot => {
+                sized(crate::ui::window::plot::view_window(&self.plot_dialog), 660, 540)
+            }
             super::super::ModalKind::LayoutManager => {
                 let i = self.active_tab;
                 let layouts = self.tabs[i].scene.layout_names();