feat: improve live update and upload feedback

Refresh release metadata immediately before downloading an update and keep automatic checks current while the app remains open.

Accept desktop file drops from the first renderer frame, preserve early and rapid drops until initialization completes, and show the live remaining upload size in the sidebar.

Add regression coverage for update freshness, startup drag-and-drop ordering, localization, and remaining-byte retry behavior. Bump the application to v2.1.25.

tests/startup-renderer.test.js

@@ -103,3 +103,24 @@ test('startup load forwards navigation options before the renderer becomes visib
 
   assert.deepEqual(startup.window.loadOptions, options);
 });
+
+test('desktop drag and drop is accepted before asynchronous renderer initialization', () => {
+  const projectRoot = path.join(__dirname, '..');
+  const appSource = fs.readFileSync(path.join(projectRoot, 'renderer', 'app.js'), 'utf8');
+  const earlyBinding = appSource.lastIndexOf('\nsetupDragDrop();');
+  const initialization = appSource.lastIndexOf('\ninit().then(');
+
+  assert.notEqual(earlyBinding, -1);
+  assert.notEqual(initialization, -1);
+  assert.ok(earlyBinding < initialization);
+  assert.match(appSource, /dataTransfer\.dropEffect\s*=\s*['"]copy['"]/u);
+});
+
+test('upload sidebar renders and updates the remaining upload size', () => {
+  const projectRoot = path.join(__dirname, '..');
+  const html = fs.readFileSync(path.join(projectRoot, 'renderer', 'index.html'), 'utf8');
+  const appSource = fs.readFileSync(path.join(projectRoot, 'renderer', 'app.js'), 'utf8');
+
+  assert.match(html, /Verbleibende Größe[\s\S]*id="uploadTelemetryRemainingSize"[^>]*>0 B</u);
+  assert.match(appSource, /_setUploadTelemetryText\(['"]uploadTelemetryRemainingSize['"],\s*formatBytes\(stats\.bytesRemaining\)\)/u);
+});