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

astro.config.mjs

@@ -1,5 +1,9 @@
 // @ts-check
+import { fileURLToPath } from 'node:url';
 import { defineConfig } from 'astro/config';
+
+const srcDir = fileURLToPath(new URL('./src', import.meta.url));
+const libDir = fileURLToPath(new URL('./src/lib', import.meta.url));
 import preact from '@astrojs/preact';
 
 // https://astro.build/config
@@ -17,6 +21,12 @@ export default defineConfig({
   
   // Vite configuration for development
   vite: {
+    resolve: {
+      alias: {
+        '@': srcDir,
+        '@lib': libDir,
+      },
+    },
     define: {
       'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
     },