Measure paper-space dimensions through the viewport they were picked in

DIMLINEAR / DIMALIGNED / DIMRADIUS / DIMDIAMETER / DIMANGULAR created on a
sheet now report the model measurement of the geometry seen through a
viewport, at any viewport scale, while definition points, the dimension line
and the text stay in paper coordinates and the annotation keeps its sheet
size (DIMSCALE is untouched).

A viewport frame is a similarity - uniform scale plus in-plane twist - so
projecting the model span onto the paper axis and compensating gives exactly
the raw paper measurement times 1/scale. No geometry is rewritten: the
compensation is persisted once as a negative DIMLFAC override on the
dimension and applied once by the linear formatter, so preview text,
dimension text, the properties measurement row and DXF/DWG export all agree.
User measurement multipliers fold into the same magnitude, and an explicit
text override still bypasses formatting entirely, so it is never re-scaled.
Angular dimensions are never compensated - a similarity preserves angles.

Mixed input (one point through viewport A, another through viewport B or on
the sheet) is refused rather than silently mis-measured: the command line
explains why and the dimension falls back to plain paper measurement.

A dimension measured through a viewport is left unassociated: its definition
points are projected paper coordinates, so inferring a paper-space
association would bind it to geometry that is not there. PR3 records the real
dimension -> viewport -> entity chain.

The result is one ordinary dimension entity carrying one style override, so
undo/redo works through the existing history with no new out-of-document
state.

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

src/modules/annotate/angular_dim.rs

@@ -482,6 +482,12 @@ impl CadCommand for AngularDimensionCommand {
         CmdResult::Cancel
     }
 
+    /// PR2: points and object picks may come through a paper-space viewport;
+    /// the committed dimension then reports the model measurement.
+    fn measures_through_viewports(&self) -> bool {
+        true
+    }
+
     fn on_escape(&mut self) -> CmdResult {
         CmdResult::Cancel
     }