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/README.md

@@ -0,0 +1,46 @@
+# New Game Wizard (`@lib/features/new-game`)
+
+Composable building blocks for the multi-step "start a new game" workflow.
+
+## Exports
+
+- `Player1Step`, `Player2Step`, `Player3Step` – Player name capture with history + quick picks.
+- `GameTypeStep` – Game type selector.
+- `RaceToStep` – Numeric race-to chooser with infinity support.
+- `BreakRuleStep`, `BreakOrderStep` – Break configuration helpers.
+- `PlayerSelectModal` – Modal surface for long player lists.
+
+All exports are surfaced via `@lib/features/new-game`.
+
+## Props & Contracts
+
+- Steps expect pure callbacks (`onNext`, `onCancel`) and derive their own UI state.
+- Player history arrays control quick-pick ordering. Empty arrays fall back gracefully.
+- Styling is shared via `NewGame.module.css` to keep a consistent visual language.
+
+## Integrating the Wizard
+
+```tsx
+import { Player1Step, Player2Step } from '@lib/features/new-game';
+import { useNewGameWizard } from '@lib/state';
+
+const wizard = useNewGameWizard();
+
+return (
+  <>
+    {wizard.newGameStep === 'player1' && (
+      <Player1Step
+        playerNameHistory={playerHistory}
+        onNext={(name) => {
+          wizard.updateGameData({ player1: name });
+          wizard.nextStep('player2');
+        }}
+        onCancel={wizard.resetWizard}
+      />
+    )}
+    {/* render subsequent steps analogously */}
+  </>
+);
+```
+
+