feat(article-export): render PDF with embedded CJK font instead of canvas

Embed SourceHanSansSC and use native jsPDF text rendering for crisp,
selectable PDF output, replacing the canvas rasterization approach.
Also fix download menu item alignment.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/views/ArticleEditorView.vue

@@ -779,11 +779,19 @@ onBeforeUnmount(() => {
 .article-editor-view__download-menu :deep(.ant-dropdown-menu-item) {
   min-width: 170px;
   padding: 11px 14px;
-  gap: 12px;
   color: #1f2937;
   font-size: 15px;
 }
 
+.article-editor-view__download-menu :deep(.ant-dropdown-menu-title-content) {
+  display: flex;
+  align-items: center;
+  justify-content: flex-start;
+  gap: 12px;
+  width: 100%;
+  text-align: left;
+}
+
 .article-editor-view__download-icon {
   display: inline-flex;
   align-items: center;