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/lib/state/index.ts

@@ -0,0 +1,8 @@
+export { useGameState } from './useGameState';
+export {
+  useModal,
+  useValidationModal,
+  useCompletionModal,
+} from './useModal';
+export { useNavigation, useNewGameWizard } from './useNavigation';
+