feat: responsive system, engineering infra, new components, performance

- Section: responsive prop with media query injection
- visual-weights: fontSize clamp() for responsive sizing
- variables.css: add border-radius/shadow/transition/z-index tokens
- ESLint flat config + Prettier + Changeset init
- New components: Footer, NewsSidebar, BreakingNewsBanner
- Image/Figure: loading=lazy, aspectRatio, sizes props

eslint.config.js

@@ -0,0 +1,22 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import react from 'eslint-plugin-react';
+import reactHooks from 'eslint-plugin-react-hooks';
+
+export default tseslint.config(
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    files: ['**/*.{ts,tsx}'],
+    plugins: { react, 'react-hooks': reactHooks },
+    rules: {
+      'react/react-in-jsx-scope': 'off',
+      '@typescript-eslint/no-unused-vars': ['warn', { argsIgnorePattern: '^_' }],
+      '@typescript-eslint/no-explicit-any': 'warn',
+      'react-hooks/rules-of-hooks': 'error',
+      'react-hooks/exhaustive-deps': 'warn',
+    },
+    settings: { react: { version: 'detect' } },
+  },
+  { ignores: ['**/dist/**', '**/node_modules/**', '**/.next/**', '**/out/**', 'packages/docs/**'] },
+);