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/features/new-game/steps/PlayerSelectModal.tsx

@@ -0,0 +1,28 @@
+import { h } from 'preact';
+import modalStyles from '../PlayerSelectModal.module.css';
+
+interface PlayerSelectModalProps {
+  players: string[];
+  onSelect: (player: string) => void;
+  onClose: () => void;
+}
+
+export const PlayerSelectModal = ({ players, onSelect, onClose }: PlayerSelectModalProps) => (
+  <div className={modalStyles.modalOverlay} onClick={onClose}>
+    <div className={modalStyles.modalContent} onClick={e => e.stopPropagation()}>
+      <div className={modalStyles.modalHeader}>
+        <h3>Alle Spieler</h3>
+        <button className={modalStyles.closeButton} onClick={onClose}>×</button>
+      </div>
+      <div className={modalStyles.playerList}>
+        {players.map(player => (
+          <button key={player} className={modalStyles.playerItem} onClick={() => onSelect(player)}>
+            {player}
+          </button>
+        ))}
+      </div>
+    </div>
+  </div>
+);
+
+