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/docs/architecture.md

@@ -0,0 +1,64 @@
+# BSC Score Modular Architecture
+
+This document captures the reusable module layout introduced in the refactor.  
+Everything under `src/lib` is now consumable from other React/Preact hosts without depending on the Astro shell that ships in this repository.
+
+## Module Overview
+
+- `@lib/domain` – **Pure domain logic** (types, constants, validation helpers, formatters).  
+  No framework dependencies, no browser APIs. Safe to re-use from Node or tests.
+- `@lib/data` – **Persistence services** (IndexedDB access, repository abstractions, test harness).  
+  Wraps browser APIs and isolates side-effects away from UI/state.
+- `@lib/state` – **Composable hooks** that orchestrate domain + data layers.  
+  Exported hooks expose serialisable state and imperative actions.
+- `@lib/ui` – **Stateless presentational primitives** (buttons, cards, layout shell, generic modals).  
+  Ship with co-located CSS modules and type-safe props.
+- `@lib/features/*` – **Feature bundles** that compose UI + state to deliver end-user flows.  
+  Current bundles:
+  - `game-list` (list + filter experience)
+  - `game-detail` (scoreboard with break tracking)
+  - `game-lifecycle` (completion modal + rematch workflow)
+  - `new-game` (wizard steps and player pickers)
+
+## Import Surfaces
+
+All entry points are re-exported via `@lib/index.ts`, so consumers can either:
+
+```ts
+import { GameService, useGameState, GameList } from '@lib';
+```
+
+or pick a scoped module:
+
+```ts
+import { GameService } from '@lib/data';
+import { GameList } from '@lib/features/game-list';
+```
+
+## Cross-Cutting Rules
+
+- **Domain first**: New feature logic should be expressed with domain types and helpers before touching hooks/UI.
+- **One-way dependencies**:
+  ```
+  domain → data → state → features → app shell
+  ```
+  Lower layers must not import from higher ones.
+- **CSS modules stay co-located** with the component they style. Consumers receive the compiled class names via the exported component props.
+- **Documentation lives next to code**: every module has a `README.md` describing intent, public API, and integration notes.
+
+## Migration Notes
+
+- Legacy `src/components` now only hosts the Astro shell (`App.tsx`, `BscScoreApp.astro`, etc.).  
+  All reusable React pieces were migrated under `src/lib`.
+- Path aliases:
+  - `@/*` → `src/*`
+  - `@lib/*` → `src/lib/*`
+  Update your editor/tsconfig if you embed these modules elsewhere.
+- Tests should import from `@lib` to avoid depending on Astro-specific wiring.
+
+## Next Steps
+
+- Promote more feature-level Storybook / Playwright fixtures into `src/lib/docs`.
+- When adding new modules, extend `src/lib/index.ts` and document usage in the corresponding folder.
+
+