feat(core)!: introduce runtime extension registry and flat module conventions

BREAKING CHANGE: sup config now derives entries from package.json#exports and a server/client glob instead of manual lists; module structure follows flat + barrel convention with .server.js/.client.js runtime suffixes

src/shared/components/Modal.js

@@ -1,6 +1,6 @@
 import React from 'react';
 import { Dialog } from '@headlessui/react';
-import { Cancel01Icon } from '../Icons';
+import { Cancel01Icon } from '../icons/index.js';
 import Button from './Button';
 
 const Modal = ({