fix: Insert Section visible in SECTION-TAB context menu

JSX rendering menu at line 17500 lacked the
!sessionTabs.some(s => s.id === activeTab) guard.
Added it - section tab context menu no longer offers
Insert Section (sections cannot contain section items).

app/static/js/app.jsx

@@ -17497,7 +17497,7 @@ const App = () => {
     className: "h-px bg-zinc-700 my-1"
   }), /*#__PURE__*/React.createElement("div", {
     className: "px-3 py-0.5 text-[10px] text-zinc-500 font-bold uppercase tracking-wider"
-  }, "Insert"), /*#__PURE__*/React.createElement("button", {
+  }, "Insert"), !sessionTabs.some(s => s.id === activeTab) && /*#__PURE__*/React.createElement("button", {
     onClick: () => { insertSectionAtPlayhead(); closeContextMenu(); },
     className: "w-full px-3 py-1.5 text-xs text-zinc-200 hover:bg-zinc-700 text-left flex items-center gap-2"
   }, /*#__PURE__*/React.createElement("span", {