feat: allow active update downloads to be canceled

Keep the dialog cancel action available during update downloads, abort the active network stream, and surface a clean canceled state with retry support. Normalize cancellation across updater, main process, renderer, and translations with regression coverage.

lib/updater.js

@@ -359,9 +359,10 @@ async function prepareUpdate(onProgress, options = {}) {
     return prepared;
 
   } catch (err) {
+    const failure = signal.aborted ? new Error('Update abgebrochen') : err;
     if (stagedInstallerPath) fs.rmSync(stagedInstallerPath, { force: true });
-    if (onProgress) onProgress({ stage: 'error', error: err.message });
-    throw err;
+    if (onProgress) onProgress({ stage: signal.aborted ? 'aborted' : 'error', error: failure.message });
+    throw failure;
   } finally {
     activeAbort = null;
   }
@@ -387,10 +388,9 @@ function launchPreparedUpdate(prepared, options = {}) {
 }
 
 function abortUpdate() {
-  if (activeAbort) {
-    activeAbort.abort();
-    activeAbort = null;
-  }
+  if (!activeAbort) return false;
+  activeAbort.abort();
+  return true;
 }
 
 module.exports = { checkForUpdate, fetchGithubReleaseNotes, prepareUpdate, launchPreparedUpdate, abortUpdate, isNewer, resolveReleaseVersion, pickSetupAsset, parseLatestYml, createUpdateAnnouncementState };