Keep the persisted representation and the seam tests consistent

Colocated unit tests pin the persisted representation: a 1:10 viewport with
no user factor writes DIMLFAC -10, a 10-unit paper span then formats as 100,
and the same dimension read back in model space does not scale. A positive
user factor folds into the magnitude, and a drawing-wide negative DIMLFAC
that already carries the compensation writes no override at all. Another
test pins the viewport model->paper affine against ViewportFrame's own
mapping, so object-pick projection and snap projection cannot drift.

Also clears the recorded snaps when a multi-dimension command commits.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/app/command_driver.rs

@@ -2254,6 +2254,7 @@ impl OpenCADStudio {
                 }
             }
             CmdResult::CommitDimensionsAndExit(dimensions) => {
+                self.clear_dimension_accepted_snaps();
                 let association_mode = self.tabs[i]
                     .scene
                     .document

src/scene/viewport_dim_seam.rs

@@ -409,9 +409,7 @@ mod tests {
             DVec3::new(940.5, 2113.25, 0.0),
         ] {
             let expected = f.model_to_paper(model);
-            let actual = t.transform_point(&acadrust::types::Vector3::new(
-                model.x, model.y, model.z,
-            ));
+            let actual = t.apply(acadrust::types::Vector3::new(model.x, model.y, model.z));
             assert!(
                 (actual.x - expected.x).abs() < 1e-9 && (actual.y - expected.y).abs() < 1e-9,
                 "{actual:?} != {expected:?}"