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/Loading.js

@@ -1,7 +1,7 @@
 'use client';
 
 import React from 'react';
-import { Recycle03Icon } from '../Icons';
+import { Recycle03Icon } from '../icons/index.js';
 
 const Loading = ({ size = 'md' }) => {
     const sizes = {