fix(userscript): defer initialization until DOM is ready

build.js

@@ -5,7 +5,7 @@ const userscriptBanner = `// ==UserScript==
 // @name         Gemini NanoBanana Watermark Remover
 // @name:zh-CN   Gemini NanoBanana 图片水印移除
 // @namespace    https://github.com/journey-ad
-// @version      0.1.2
+// @version      0.1.3
 // @description  Automatically removes watermarks from Gemini AI generated images
 // @description:zh-CN 自动移除 Gemini AI 生成图像中的水印
 // @icon         https://www.google.com/s2/favicons?domain=gemini.google.com
@@ -16,7 +16,7 @@ const userscriptBanner = `// ==UserScript==
 // @match        https://gemini.google.com/u/*/app
 // @match        https://gemini.google.com/u/*/app/*
 // @grant        GM_xmlhttpRequest
-// @run-at       document-start
+// @run-at       document-end
 // ==/UserScript==
 `;