Refactor signup process and enhance OAuth handling

- Updated signup-page.js to support additional message types for signup entry and password page readiness.
- Introduced new helper functions for managing signup entry states and filling email/password.
- Enhanced error handling and logging for better debugging during the signup process.
- Modified sub2api-panel.js and vps-panel.js to handle REQUEST_OAUTH_URL messages and improved logging.
- Updated sidepanel.html to reflect changes in button labels for clarity in user actions.

sidepanel/sidepanel.html

@@ -524,17 +524,17 @@
     <div class="steps-list">
       <div class="step-row" data-step="1">
         <div class="step-indicator" data-step="1"><span class="step-num">1</span></div>
-        <button class="step-btn" data-step="1">获取 OAuth 链接</button>
+        <button class="step-btn" data-step="1">打开 ChatGPT 官网</button>
         <span class="step-status" data-step="1"></span>
       </div>
       <div class="step-row" data-step="2">
         <div class="step-indicator" data-step="2"><span class="step-num">2</span></div>
-        <button class="step-btn" data-step="2">打开注册页</button>
+        <button class="step-btn" data-step="2">注册并输入邮箱</button>
         <span class="step-status" data-step="2"></span>
       </div>
       <div class="step-row" data-step="3">
         <div class="step-indicator" data-step="3"><span class="step-num">3</span></div>
-        <button class="step-btn" data-step="3">填写邮箱和密码</button>
+        <button class="step-btn" data-step="3">填写密码并继续</button>
         <span class="step-status" data-step="3"></span>
       </div>
       <div class="step-row" data-step="4">