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 <noreply@anthropic.com>

src/command.rs

@@ -241,6 +241,8 @@ pub enum CmdResult {
     },
     /// Set the plot window on the active layout's PlotSettings.
     SetPlotWindow { p1: DVec3, p2: DVec3 },
+    /// Quick-print the bounding box of the given selected entities to a PDF.
+    QuickPrint(Vec<Handle>),
     /// Replace the text content of a Text/MText entity in-place.
     DdeditEntity { handle: Handle, new_text: String },
     /// Open the in-place editor (plain box or rich MText editor, per type) for