feat(scale): drive scales from the drawing's scale list

Read the model-space annotation scale from the standard CANNOSCALE /
CANNOSCALEVALUE header variables instead of a user-variable hack, and
populate both the status-bar scale picker and the viewport Scale
property purely from the drawing's ACAD_SCALELIST — no built-in
fallback set. Xref-derived scales (`_XREF` suffix, `name|` prefix)
are filtered out so only the host drawing's own scales appear.

Bumps the patched acadrust to the commit that adds CANNOSCALE/
CANNOSCALEVALUE read/write.

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

src/entities/viewport.rs

@@ -25,6 +25,20 @@ const STANDARD_SCALES: &[(&str, f64)] = &[
     ("10:1", 10.0),
 ];
 
+/// Parse a scale ratio name to its paper/drawing factor: "1:50" -> 0.02,
+/// "2:1" -> 2.0. Also accepts a plain decimal ("0.02").
+fn parse_scale_ratio(label: &str) -> Option<f64> {
+    if let Some((a, b)) = label.split_once(':') {
+        let n: f64 = a.trim().parse().ok()?;
+        let d: f64 = b.trim().parse().ok()?;
+        if d.abs() > 1e-12 {
+            return Some(n / d);
+        }
+        return None;
+    }
+    label.trim().parse::<f64>().ok()
+}
+
 fn scale_label(scale: f64) -> String {
     for (label, val) in STANDARD_SCALES {
         if (scale - val).abs() < val * 0.01 {
@@ -411,9 +425,11 @@ fn apply_geom_prop(vp: &mut Viewport, field: &str, value: &str) {
         _ => {}
     }
 
-    // Standard scale picker.
+    // Scale picker. The label is a ratio name from the drawing's scale list
+    // ("1:50", "2:1"); parse it to the paper/drawing factor so any named
+    // scale resolves, not just the built-in set.
     if field == "vscale_std" {
-        if let Some(&(_, scale)) = STANDARD_SCALES.iter().find(|(label, _)| *label == value) {
+        if let Some(scale) = parse_scale_ratio(value) {
             vp.custom_scale = scale;
             if scale > 1e-9 {
                 vp.view_height = vp.height / scale;