Options: snap marker size (#1770)

The object-snap glyphs were fixed at 5 px; a Drafting slider now scales
them from 1 to 20 px.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/config.rs

@@ -369,6 +369,8 @@ pub struct ModelSpaceThemeConfig {
     pub grip_hot: u8,
     /// GRIPHOVER: hovered/warm grip ACI color (0 = Theme Primary Strong, 1..=255 = ACI).
     pub grip_hover: u8,
+    /// SNAPMARKERSIZE: object-snap marker half-size in pixels (1–20, default 5).
+    pub snap_marker_size: u8,
 }
 
 impl Default for ModelSpaceThemeConfig {
@@ -390,6 +392,7 @@ impl Default for ModelSpaceThemeConfig {
             grip_color: 0,
             grip_hot: 0,
             grip_hover: 0,
+            snap_marker_size: 5,
         }
     }
 }