feat(plot): QUICKPRINT/QP — plot a selection's bounding box to PDF (#325)

Run QUICKPRINT (or QP), select objects, then Enter: the selection's
bounding box becomes the plot window and a PDF is written next to the
drawing (<name>_<timestamp>.pdf) using the active page setup, with no
dialog. Model space.

Implemented as a selection-gathering CadCommand (src/modules/view/
quick_print.rs) returning CmdResult::QuickPrint(handles); the host
(on_quick_print_handles) unions the picked entities' AABBs, sets the
plot window, and reuses the tested clipped window-export path.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/command_driver.rs

@@ -1235,6 +1235,13 @@ impl OpenCADStudio {
                 self.tabs[i].scene.clear_preview_wire();
                 self.restore_pre_cmd_tangent();
             }
+            CmdResult::QuickPrint(handles) => {
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.tabs[i].scene.clear_preview_wire();
+                self.restore_pre_cmd_tangent();
+                return self.on_quick_print_handles(handles);
+            }
             CmdResult::StretchEntities {
                 handles,
                 win_min,