refactor: extract reusable library

- move reusable domain, data, state, ui code into src/lib
- update host screens to consume new library exports
- document architecture and configure path aliases
- bump astro integration dependencies for compatibility

Refs #30

src/components/ui/Button.tsx

@@ -1,5 +1,5 @@
 import { h } from 'preact';
-import type { ButtonProps } from '../../types/ui';
+import type { ButtonProps } from '@lib/ui/types';
 import styles from './Button.module.css';
 
 export function Button({