feat(account): add managed credits and cloud gateway

Introduce optional Apple account-backed credits with scoped gateway access while preserving local and BYOK paths. Refresh assistant behavior, tests, privacy disclosures, docs, and the website for the 2.0 experience.

docs/osgkeyboardversion.html

@@ -176,6 +176,51 @@
   <p class="empty" id="empty-zh">暂无与当前版本匹配的更新说明。</p>
   <p class="empty" id="empty-en">No release notes match this app version.</p>
 
+  <!-- ========== 2.0.0 ========== -->
+  <article class="version-block" data-version="2.0.0">
+    <div class="version-chip">2.0.0</div>
+
+    <div class="lang-block" data-lang="zh">
+      <section class="section">
+        <h2>可选 OSG 账号</h2>
+        <ul>
+          <li>新增 Apple 登录、账号资料管理和 App 内账号注销</li>
+          <li>新增托管积分、App Store 积分包与邀请功能</li>
+          <li>登录后可使用托管云端语音与 AI 服务；本地听写和用户自备 API Key 无需账号，仍可独立使用</li>
+        </ul>
+      </section>
+
+      <section class="section">
+        <h2>助手体验升级</h2>
+        <ul>
+          <li>语音与 AI 合并为统一的助手入口，并根据当前输入框显示对应操作</li>
+          <li>AI 回答仅在输入框与光标上下文仍匹配时自动插入，避免写入错误位置</li>
+          <li>修正退出登录与注销账号确认弹窗的锚点位置</li>
+        </ul>
+      </section>
+    </div>
+
+    <div class="lang-block" data-lang="en">
+      <section class="section">
+        <h2>Optional OSG Account</h2>
+        <ul>
+          <li>Adds Sign in with Apple, profile controls, and in-app account deletion</li>
+          <li>Adds managed credits, App Store credit packs, and referrals</li>
+          <li>Signed-in users can use managed cloud speech and AI; local dictation and user-owned provider keys remain independent and require no account</li>
+        </ul>
+      </section>
+
+      <section class="section">
+        <h2>Assistant Improvements</h2>
+        <ul>
+          <li>Combines Voice and AI into one Assistant entry with actions adapted to the focused field</li>
+          <li>Inserts AI answers automatically only while the original field and cursor context still match</li>
+          <li>Fixes the anchors for sign-out and account-deletion confirmation dialogs</li>
+        </ul>
+      </section>
+    </div>
+  </article>
+
   <!-- ========== 1.8.0 ========== -->
   <article class="version-block" data-version="1.8.0">
     <div class="version-chip">1.8.0</div>