feat(render): boost model-space lineweight display for legibility (#147)

Lineweights were rendered at their true physical size (mm × 96/25.4 px),
which is ~2 px for a 0.5 mm line — too timid to tell weights apart, and
every weight ≤ 0.25 mm floored to 1 px (no visible difference). Other DWG
editors display model-space lineweights larger than true size for screen
legibility; apply the same 2× boost so weights are pronounced and
distinguishable.

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

src/scene/view/render.rs

@@ -523,9 +523,16 @@ pub(in crate::scene) fn render_style_for(
             _ => ew,
         };
         const MM_TO_PX: f32 = 96.0 / 25.4;
+        // CAD apps display model-space lineweights larger than their true
+        // physical size so the gradations stay legible on screen — at true
+        // scale a 0.5 mm line is ~2 px and is indistinguishable from thinner
+        // weights (which all floor to 1 px). Apply the same legibility boost so
+        // weights are pronounced and tell apart, matching other DWG editors.
+        // (#147)
+        const LWT_DISPLAY_BOOST: f32 = 2.0;
         resolved
             .millimeters()
-            .map(|mm| (mm as f32 * MM_TO_PX).max(1.0))
+            .map(|mm| (mm as f32 * MM_TO_PX * LWT_DISPLAY_BOOST).max(1.0))
             .unwrap_or(1.0)
     };