fix(ui): unify dialogs and complete theme component coverage

frontend/src/features/themes/themeSpecimen.html

@@ -0,0 +1,19 @@
+<div class="theme-specimen">
+  <div class="form-grid">
+    <label class="field">单行输入<input class="input" placeholder="输入内容" /></label>
+    <label class="field">下拉选择<select class="select"><option>选项一</option><option>选项二</option></select></label>
+    <label class="field">禁用输入<input class="input" value="不可编辑" disabled /></label>
+    <label class="field">多行文本<textarea class="textarea" rows="3">第一行
+第二行
+第三行</textarea></label>
+  </div>
+  <div class="inline-actions"><button class="button-primary">主要按钮</button><button class="button-secondary">次要按钮</button><button class="button-danger">危险操作</button><button class="button-primary" disabled>禁用按钮</button><span class="badge success">成功标签</span><span class="badge warning">提醒</span></div>
+  <p class="error-banner" role="alert">错误状态示例：请检查输入内容。</p>
+  <details class="ui-disclosure"><summary>折叠内容</summary><p>展开后检查箭头、边框与文字颜色。</p></details>
+  <details open class="ui-disclosure"><summary>展开内容</summary><p>这段文字用于查看当前主题的展开样式。</p></details>
+  <section class="surface-nested"><h3>嵌套卡片</h3><p>嵌套内容使用轻量边框，避免重复装饰。</p></section>
+  <section class="specimen-markdown"><h2>Markdown 样例</h2><p>正文、<strong>粗体</strong>、<em>斜体</em>、<del>删除线</del>和 <code>inline code</code>。</p><blockquote>引用内容</blockquote><pre><code>const note = "主题预览";
+console.log(note);</code></pre><table><thead><tr><th>名称</th><th>状态</th></tr></thead><tbody><tr><td>长内容示例</td><td>已完成</td></tr></tbody></table></section>
+  <figure class="specimen-chart"><figcaption>数据配色示例</figcaption><div role="img" aria-label="本地用量 30，提供商用量 70"><span style="height:30%;background:var(--color-accent-primary)"></span><span style="height:70%;background:var(--color-accent-secondary)"></span></div></figure>
+  <p class="subtle specimen-long">超长模型标识：provider/model-with-a-very-long-identifier-for-layout-validation-012345678901234567890123456789</p>
+</div>