fix(scene): viewport auto-fit fallback + f64-precision projection

Three changes to make paper-space viewports render correctly on
UTM-scale drawings whose viewports were saved with default
view_target=(0, 0, 0) and a view_center pointing at empty WCS:

1. **Auto-fit fallback.** When the saved view's WCS rect doesn't
   overlap the IQR-bounded content cluster (`world_offset ±
   local_extent_max`), override `view_center` with `world_offset` and
   recompute `view_height` to fit the cluster into the paper viewport.
   Matches AutoCAD's silent auto-fit-on-open for stale / uninitialized
   viewports; without it those viewports rendered blank.

2. **f64 projection inner loop.** The previous f32 path computed
   `(wire_offset_rel - target_offset_rel).dot(view_right) -
   view_center` by subtracting values at ~5e6 magnitude (f32 ULP
   ~0.5 m) to land on a small paper offset. The cancellation produced
   centimetre-scale jitter on paper output even when the model was
   clean. Reconstruct the wire WCS coord, subtract the display center,
   and dot-project in f64; cast to f32 only at the final paper
   position where magnitudes are bounded by the viewport rect.

3. **examples/inspect_viewports.rs** — diagnostic that dumps every
   viewport's saved view fields (view_target, view_center, view_height
   vs paper height, custom_scale, status flags) plus drawing-level
   insertion_units and model-space extents. Used to verify that
   acadrust's DWG reader reads view_height correctly; the
   `view_height == vp.height` patterns observed on real files turn out
   to be genuine "default 1:1" file content rather than a reader bug
   (a round-trip test through DwgWriter / DwgReader survives all
   per-viewport values).

Also: switch the `acadrust` patch from `HakanSeven12/acadrust@feat/
expose-blockrecord-is-loaded` (a stale branch with the abandoned
is_loaded experiment) to `hakanaktt/acadrust@main`. Upstream main
now carries the layout paper-dimensions and mirrored-arc fixes that
this branch used to add — plus PR #20's DXF reading fixes that the
old branch was missing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -41,7 +41,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.3.4"
-source = "git+https://github.com/HakanSeven12/acadrust?branch=feat%2Fexpose-blockrecord-is-loaded#44ee57604af6f29a3f3ace05c2e49879fb8ae18a"
+source = "git+https://github.com/hakanaktt/acadrust?branch=main#ee5f0db7f8159ea39db3c4a85dd58bec9aceb121"
 dependencies = [
  "ahash",
  "anyhow",