feat(seo-geo): 全页面 SEO/GEO 回填、统一检查与 Plaza 注入

引入批量回填与审计工具链，强制 mindspace-geo 元数据，扩展 sitemap/llms 收录 /learn，并为 Plaza 壳页注入 canonical/OG/JSON-LD；本地 593 页已通过 check:mindspace-cover。

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

server/portal-seo-discovery-routes.mjs

@@ -50,10 +50,13 @@ export function attachPortalSeoDiscoveryRoutes(
       return res.status(503).type('text/plain; charset=utf-8').send('SEO discovery unavailable\n');
     }
     const origin = resolveRequestOrigin(req);
-    const entries = await service.listIndexablePublications(pool, {
+    const publications = await service.listIndexablePublications(pool, {
       limit: req.query.limit,
       offset: req.query.offset,
     });
+    const entries = service.mergeDiscoveryEntries
+      ? service.mergeDiscoveryEntries(publications)
+      : publications;
     return res
       .type('application/xml; charset=utf-8')
       .set('Cache-Control', 'public, max-age=300')
@@ -72,10 +75,13 @@ export function attachPortalSeoDiscoveryRoutes(
       return res.status(503).type('text/plain; charset=utf-8').send('GEO discovery unavailable\n');
     }
     const origin = resolveRequestOrigin(req);
-    const entries = await service.listIndexablePublications(pool, {
+    const publications = await service.listIndexablePublications(pool, {
       limit: req.query.limit,
       offset: req.query.offset,
     });
+    const entries = service.mergeDiscoveryEntries
+      ? service.mergeDiscoveryEntries(publications)
+      : publications;
     return res
       .type('text/plain; charset=utf-8')
       .set('Cache-Control', 'public, max-age=300')