fix: hide #view-apidocs when [hidden] attribute is set

#view-apidocs has 'display: flex' in CSS which overrides the browser's
default '[hidden] { display: none }' user-agent style, causing the API
docs iframe to remain visible and bleed into the LLM config page.

Fix: add explicit '#view-apidocs[hidden] { display: none }' rule.
Also exclude apidocs from @media print to prevent iframe printing.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

webapp/static/css/app.css

@@ -310,6 +310,7 @@ table.group-table td { border-bottom: 1px solid #f1f5f9; font-variant-numeric: t
 
 /* ---------- API 文档 iframe ---------- */
 #view-apidocs { padding: 0; display: flex; flex-direction: column; flex: 1; }
+#view-apidocs[hidden] { display: none; }
 .apidocs-frame {
   flex: 1;
   width: 100%;
@@ -404,6 +405,7 @@ table.group-table td { border-bottom: 1px solid #f1f5f9; font-variant-numeric: t
   .app { display: block; }
   .main { display: block; width: 100%; }
   .view { padding: 0; display: block !important; }
+  #view-apidocs { display: none !important; }  /* never print the API docs iframe */
   #view-report { display: block !important; }
 
   /* ── 报告内容 ── */