fix: use nonzero fill rule instead of evenodd

evenodd creates transparent stripes where polygon rings overlap at
certain latitudes. nonzero fills correctly regardless of ring overlap.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

layouts/shortcodes/world-map.html

@@ -123,7 +123,7 @@
         });
       }
     });
-    ctx.fill('evenodd');
+    ctx.fill('nonzero');
 
     // Pass 2: overdraw colored countries only
     geoData.features.forEach(function(f) {
@@ -154,7 +154,7 @@
     } else if (geom.type === 'LineString') {
       traceLine(ctx, geom.coordinates, sx, sy);
     }
-    if (fill) ctx.fill('evenodd');
+    if (fill) ctx.fill('nonzero');
     else ctx.stroke();
   }