fix: revoke object URL, merge history on import, handle prompt cancel

js/collection.js

@@ -43,6 +43,7 @@ export function addToHistory(hsl) {
 
 export function addColorToSchema(hsl) {
   const name = prompt('Schema-Name (leer = letztes Schema):');
+  if (name === null) return; // user pressed Cancel — do nothing
   const data = load();
   if (name) {
     const existing = data.schemata.find(s => s.name === name);
@@ -83,10 +84,14 @@ export function deleteSchema(name) {
 export function exportCollection() {
   const data = load();
   const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' });
+  const url = URL.createObjectURL(blob);
   const a = document.createElement('a');
-  a.href = URL.createObjectURL(blob);
+  a.href = url;
   a.download = 'farbhelfer-sammlung.json';
+  document.body.appendChild(a);
   a.click();
+  document.body.removeChild(a);
+  URL.revokeObjectURL(url);
 }
 
 export function importCollection() {
@@ -109,6 +114,11 @@ export function importCollection() {
         (imported.schemata || []).forEach(s => {
           if (!existingSchemaNames.has(s.name)) data.schemata.push(s);
         });
+        const existingHistHexes = new Set(data.history.map(hslToHex));
+        (imported.history || []).forEach(hsl => {
+          if (!existingHistHexes.has(hslToHex(hsl))) data.history.push(hsl);
+        });
+        if (data.history.length > 20) data.history = data.history.slice(0, 20);
         save(data);
         renderSammlung();
         alert('Import erfolgreich.');