feat: support Cloud Mail email provider

- Merge the latest dev branch into PR #212 for a clean dev-targeted review base.

- Add Cloud Mail/SkyMail provider support for email generation and verification-code polling.

- Move Cloud Mail runtime logic into a dedicated background module and add docs plus regression tests.

sidepanel/sidepanel.html

@@ -179,7 +179,7 @@
       <div class="data-row" id="row-sub2api-url" style="display:none;">
         <span class="data-label">SUB2API</span>
         <input type="text" id="input-sub2api-url" class="data-input"
-          placeholder="https://sub2api.hisence.fun/admin/accounts" />
+          placeholder="https://your-sub2api-domain/admin/accounts" />
       </div>
       <div class="data-row" id="row-sub2api-email" style="display:none;">
         <span class="data-label">账号</span>
@@ -406,10 +406,10 @@
             <option value="hotmail-api">Hotmail（账号池）</option>
             <option value="luckmail-api">LuckMail（API 购邮）</option>
             <option value="icloud">iCloud 邮箱</option>
-            <option value="163">163 邮箱 (mail.163.com)</option>
-            <option value="163-vip">163 VIP 邮箱 (vip.163.com)</option>
-            <option value="126">126 邮箱 (mail.126.com)</option>
-            <option value="qq">QQ 邮箱 (wx.mail.qq.com)</option>
+            <option value="163">163 邮箱 (mail.163.com) 下个版本删除</option>
+            <option value="163-vip">163 VIP 邮箱 (vip.163.com) 下个版本删除</option>
+            <option value="126">126 邮箱 (mail.126.com) 下个版本删除</option>
+            <option value="qq">QQ 邮箱 (wx.mail.qq.com) 下个版本删除</option>
             <option value="inbucket">Inbucket（自定义主机）</option>
             <option value="2925">2925 邮箱 (2925.com)</option>
             <option value="gmail">Gmail 邮箱 (mail.google.com)</option>