fix: nav editor API calls use workspace api() signature (url, method, data)

The api() helper takes positional args, not fetch-style options object.
This caused 'not a valid HTTP method' error on save/publish.

Co-Authored-By: Claude Code <noreply@anthropic.com>

app/static/workspace.js

@@ -357,7 +357,7 @@ async function saveNavDraft(){
  const s=state.site;if(!s||!navSiteDesign)return;
  try{
   navSiteDesign.nav=navItems;
-  const r=await api(`/api/sites/${s.id}/site-design`,{method:'PUT',headers:{'Content-Type':'application/json'},body:JSON.stringify({config:navSiteDesign,expected_revision:navDesignRevision})});
+  const r=await api(`/api/sites/${s.id}/site-design`,'PUT',{config:navSiteDesign,expected_revision:navDesignRevision});
   navDesignRevision=r.revision||navDesignRevision+1;
   toast('导航草稿已保存，点击「发布导航」使其参与下一次构建');
  }catch(e){toast('保存失败：'+e.message,true)}
@@ -366,7 +366,7 @@ async function publishNav(){
  const s=state.site;if(!s||!navSiteDesign)return;
  try{
   await saveNavDraft();
-  await api(`/api/sites/${s.id}/site-design/publish`,{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({expected_revision:navDesignRevision})});
+  await api(`/api/sites/${s.id}/site-design/publish`,'POST',{expected_revision:navDesignRevision});
   toast('导航已发布！重新构建网站后生效。');
   $('#navModal').close();
  }catch(e){toast('发布失败：'+e.message,true)}