fix(layout): faithful paper-space round-trip and page setup (#156)

Builds on the acadrust viewport/PlotSettings round-trip fixes:

- Write the sheet viewport's view position into view_center (DCS) with
  view_target at the origin, matching AutoCAD; the old view_target form shifted
  the layout.
- PAGESETUP now writes paper size, rotation, origin and units onto the Layout's
  embedded PlotSettings (not just a side object), and bumps geometry, so an edit
  shows on the sheet immediately and survives a save.
- Draw the printable-area guide (paper inset by plot margins, rotation-aware) as
  a dashed rectangle, matching AutoCAD's layout view.
- Plot/PDF export falls back to the Layout's embedded PlotSettings via
  effective_plot_settings(), so a loaded file's rotation/origin/scale apply.

Bumps acadrust to pick up the viewport-status and PlotSettings round-trip fixes.

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

Cargo.lock

@@ -70,7 +70,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.3.4"
-source = "git+https://github.com/HakanSeven12/acadrust?branch=main#3a1b66d7ec79fe576da465de48210d002dd52985"
+source = "git+https://github.com/HakanSeven12/acadrust?branch=main#1b97dd3d52729ddf68ad6a542efab1eac3ebe9c3"
 dependencies = [
  "ahash",
  "anyhow",