feat: remove legacy OpenCode runtime

Cut product flows over to Coding/Pi and retain only the migration-owned v1 boundary. Promote supported native optional packages because electron-builder omitted pnpm transitive optional closure from the packaged ASAR.

src/pages/Subagents/index.tsx

@@ -1,7 +1,7 @@
 import { Navigate } from 'react-router-dom';
 
 export function Subagents() {
-  return <Navigate to="/opencode-chat" replace />;
+  return <Navigate to="/chat" replace />;
 }
 
 export default Subagents;