feat: add electron app.

electron/preload/src/index.ts

@@ -0,0 +1,24 @@
+const styleStr = `.siderbar {
+  -webkit-app-region: drag;
+}
+.siderbar header h1 a, github-corners {
+  display: none;
+}
+article.content:before {
+  -webkit-app-region: drag;
+  position: absolute;
+  content: ' ';
+  display: block;
+  height: 41px;
+  width: 100%;
+  z-index: -1;
+}`;
+
+document.addEventListener('DOMContentLoaded', () => {
+  const head = document.querySelector('head');
+  const style = document.createElement('style');
+  style.textContent = styleStr;
+  if (head) {
+    head.append(style);
+  }
+});