feat(publish): render jianshu html images as markdown

Jianshu's HTML editor strips uploaded <img> tags during save, so previously
uploaded images vanished from the rendered article. After image upload,
convert each <img> (and surrounding <p> wrappers) to a markdown image block
in both the desktop and extension publish paths so the references survive.

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

packages/publisher-platforms/src/jianshu.ts

@@ -127,6 +127,46 @@ function parseJianshuErrorMessage(error: unknown, fallback: string): string {
   return fallback;
 }
 
+function extractHtmlAttribute(sourceTag: string, attributeName: string): string | null {
+  const matcher = new RegExp(`\\s${attributeName}\\s*=\\s*(?:"([^"]*)"|'([^']*)'|([^\\s"'>]+))`, "i");
+  const match = matcher.exec(sourceTag);
+  const value = match?.[1] ?? match?.[2] ?? match?.[3] ?? "";
+  const trimmed = value.trim();
+  return trimmed ? trimmed : null;
+}
+
+function escapeMarkdownAlt(value: string): string {
+  return value.replace(/\\/g, "\\\\").replace(/\]/g, "\\]");
+}
+
+function markdownImageFromHtmlTag(imgTag: string): string {
+  const src = extractHtmlAttribute(imgTag, "src");
+  if (!src) {
+    return imgTag;
+  }
+
+  const alt = extractHtmlAttribute(imgTag, "alt") ?? "";
+  return `![${escapeMarkdownAlt(alt)}](${src})`;
+}
+
+export function renderJianshuHtmlImagesAsMarkdown(content: string): string {
+  if (!/<img\b/i.test(content)) {
+    return content;
+  }
+
+  let next = content.replace(
+    /<p\b[^>]*>\s*(<img\b[^>]*\/?>)\s*<\/p>/gi,
+    (_match, imgTag: string) => `\n\n${markdownImageFromHtmlTag(imgTag)}\n\n`,
+  );
+
+  next = next.replace(
+    /<img\b[^>]*\/?>/gi,
+    (imgTag) => `\n\n${markdownImageFromHtmlTag(imgTag)}\n\n`,
+  );
+
+  return next.replace(/\n{3,}/g, "\n\n").trim();
+}
+
 export async function fetchJianshuMediaSnapshot(
   fetchJson: <T>(input: string, init?: RequestInit) => Promise<T>,
 ): Promise<JianshuMediaSnapshot | null> {
@@ -265,7 +305,7 @@ async function processContentImages(
   for (const [from, to] of replacements.entries()) {
     next = next.split(from).join(to);
   }
-  return next;
+  return renderJianshuHtmlImagesAsMarkdown(next);
 }
 
 async function attachCoverImage(