feat(cowork): re-enable Claude Cowork with preset-only stdio MCP

Restore Cowork feature while closing the RCE vector: drop user-defined
stdio commands so only hard-coded preset plugins (browsermcp) may spawn.
Custom MCP now accepts remote URL only. Routes stay gated to localhost.

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

src/app/api/mcp/[plugin]/message/route.js

@@ -5,8 +5,6 @@ export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
 export async function POST(request, { params }) {
-  // Cowork disabled: MCP stdio bridge spawns arbitrary processes (RCE risk).
-  return NextResponse.json({ error: "Cowork is disabled" }, { status: 403 });
   const { plugin } = await params;
   if (!findPlugin(plugin)) {
     return NextResponse.json({ error: `Unknown plugin: ${plugin}` }, { status: 404 });