feat(mindspace): 全部页面管理、级联删除与页面同步去重

支持全部页面分页/多选/删除/分享，删除时可选移除广场帖并清理工作区附件；修复并发同步重复创建页面，并补齐预览下载链接重写与 iframe 下载权限。

Co-authored-by: Cursor <cursoragent@cursor.com>

mindspace-page-sync.mjs

@@ -35,6 +35,23 @@ function extractHtmlSummary(content) {
   return match?.[1]?.trim().slice(0, 1000) ?? '';
 }
 
+async function findPageByWorkspaceRelativePath(pool, userId, relativePath) {
+  const [rows] = await pool.query(
+    `SELECT p.id, p.updated_at
+     FROM h5_page_records p
+     JOIN h5_page_versions pv ON pv.id = p.current_version_id
+     WHERE p.user_id = ?
+       AND p.status <> 'deleted'
+       AND JSON_UNQUOTE(JSON_EXTRACT(pv.source_snapshot_json, '$.relative_path')) = ?
+     ORDER BY p.updated_at DESC, p.id DESC
+     LIMIT 1`,
+    [userId, relativePath],
+  );
+  const row = rows[0];
+  if (!row) return null;
+  return { id: row.id, updatedAt: Number(row.updated_at ?? 0) };
+}
+
 async function loadIndexedWorkspacePages(pool, userId) {
   const [rows] = await pool.query(
     `SELECT p.id, p.updated_at, p.source_asset_id, pv.source_snapshot_json
@@ -99,6 +116,7 @@ async function listPublishPublicHtmlFiles(publishDir) {
 }
 
 async function upsertWorkspaceHtmlPage({
+  pool,
   pageService,
   userId,
   indexedPages,
@@ -109,10 +127,18 @@ async function upsertWorkspaceHtmlPage({
 }) {
   const title = extractHtmlTitle(content) || titleFromRelativePath(relativePath);
   const summary = extractHtmlSummary(content);
-  const existing =
+  let existing =
     indexedPages.get(relativePath) ??
     (assetId ? indexedPages.get(`asset:${assetId}`) : null);
 
+  if (!existing && pool) {
+    existing = await findPageByWorkspaceRelativePath(pool, userId, relativePath);
+    if (existing) {
+      indexedPages.set(relativePath, existing);
+      if (assetId) indexedPages.set(`asset:${assetId}`, existing);
+    }
+  }
+
   const pageInput = {
     title,
     summary,
@@ -186,6 +212,7 @@ export async function syncGeneratedPagesFromPublicAssets({
           continue;
         }
         const result = await upsertWorkspaceHtmlPage({
+          pool,
           pageService,
           userId,
           indexedPages,
@@ -237,6 +264,7 @@ export async function syncGeneratedPagesFromPublicAssets({
       const { path: assetPath } = await assetService.readAsset(userId, asset.id);
       const content = await fs.readFile(assetPath, 'utf8');
       const result = await upsertWorkspaceHtmlPage({
+        pool,
         pageService,
         userId,
         indexedPages,