fix: interactive popups + maxZoom 4 + invisible hit layer

Popup click/hover now uses invisible GeoJSON fill layer (raster layers
don't support events). MaxZoom capped at 4 to prevent blurry zoom.

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

static/map-embed.html

@@ -43,6 +43,7 @@ body { margin: 0; overflow: hidden; }
     zoom: 2,
     scrollZoom: false,
     fadeDuration: 0,
+    maxZoom: 4,
     style: 'https://maps.clicksports.de/styles/klokantech-basic/style.json'
   });
   _ifkMap.addControl(new maplibregl.NavigationControl({ showCompass: false }), 'top-right');
@@ -181,8 +182,12 @@ body { margin: 0; overflow: hidden; }
     renderChoropleth();
     _ifkMap.on('moveend', function() { if (needsRerender()) renderChoropleth(); });
 
-    // Keep GeoJSON source for hover/click interaction (invisible)
+    // Invisible GeoJSON layer for hover/click interaction
     _ifkMap.addSource('countries', { type: 'geojson', data: geo });
+    _ifkMap.addLayer({
+      id: 'countries-interaction', type: 'fill', source: 'countries',
+      paint: { 'fill-color': '#000000', 'fill-opacity': 0, 'fill-antialias': false }
+    });
     _ifkMap.addLayer({
       id: 'choropleth-hover', type: 'fill', source: 'countries',
       paint: { 'fill-color': '#667eea', 'fill-opacity': 0.2, 'fill-antialias': false },
@@ -191,18 +196,18 @@ body { margin: 0; overflow: hidden; }
 
     var popup = new maplibregl.Popup({ closeButton: true, closeOnClick: false, maxWidth: '280px' });
 
-    _ifkMap.on('mousemove', 'choropleth-fill', function(e) {
+    _ifkMap.on('mousemove', 'countries-interaction', function(e) {
       var id = e.features[0].properties.isoNum;
       var c = byIsoNum[id];
       _ifkMap.getCanvas().style.cursor = c ? 'pointer' : '';
       _ifkMap.setFilter('choropleth-hover', c ? ['==', 'isoNum', id] : ['==', 'isoNum', '']);
     });
-    _ifkMap.on('mouseleave', 'choropleth-fill', function() {
+    _ifkMap.on('mouseleave', 'countries-interaction', function() {
       _ifkMap.getCanvas().style.cursor = '';
       _ifkMap.setFilter('choropleth-hover', ['==', 'isoNum', '']);
     });
 
-    _ifkMap.on('click', 'choropleth-fill', function(e) {
+    _ifkMap.on('click', 'countries-interaction', function(e) {
       var id = e.features[0].properties.isoNum;
       var c = byIsoNum[id];
       if (!c) return;