fix: use Leaflet Canvas renderer instead of SVG

Canvas renders to single bitmap - no SVG layer compositing that causes
GPU seams on retina Macs. Padding 1.0 for smooth panning.

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

layouts/shortcodes/world-map.html

@@ -62,6 +62,7 @@
   var byIsoNum = {};
   countries.forEach(function(c) { byIsoNum[c.isoNum] = c; });
 
+  var canvasRenderer = L.canvas({ padding: 1.0 });
   var map = L.map('ifk-world-map', {
     center: [20, 20],
     zoom: 2,
@@ -69,7 +70,9 @@
     maxZoom: 6,
     scrollWheelZoom: false,
     attributionControl: false,
-    zoomControl: false
+    zoomControl: false,
+    renderer: canvasRenderer,
+    preferCanvas: true
   });
 
   L.control.zoom({ position: 'topright' }).addTo(map);