M4: художественный конвейер

- scripts/build-art.mjs: все спрайты игры собираются из исходников,
  а не кладутся руками. Лица карт растеризуются из векторов,
  рубашка/стол/панели/кнопки нарисованы SVG-ом прямо в скрипте
- 36 лиц 220x320 + рубашка, автоатлас 2048x2048, обрезка выключена
  (раскладка рассчитывает на точный размер карты)
- девятипатчевые плитки 120x120 с рамкой 40
- фон стола 540x960, рисуется в 2x — градиенту детализация не нужна,
  а памяти под текстуру уходит вчетверо меньше
- исходные векторы перенесены из local/ в art-src/cards
- ATTRIBUTION.md: LGPL-3.0, атрибуция обязательна; там же написано,
  что менять, если такая лицензия не подходит для релиза

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

assets/art/cards/ATTRIBUTION.md

@@ -0,0 +1,29 @@
+# Card face attribution
+
+The 36 card faces in this folder are rendered from **Vector Playing Cards** by
+**Chris Aguilar** (`totalnonsense.com/open-source-vector-playing-cards/`,
+originally `code.google.com/p/vector-playing-cards/`).
+
+- **Licence:** LGPL-3.0
+- **Attribution is a requirement of the licence** and must appear in the shipped
+  game — a credits screen, an about box, or the store listing description.
+- The unmodified vector sources are kept in [`art-src/cards`](../../../art-src/cards)
+  so the LGPL obligation to make the source form available is met, and so the
+  sprites can be regenerated: `npm run build:art`.
+
+The court cards (J, Q, K) come from the set's alternate variants, which carry the
+proper court illustrations; the plain variants are only a large suit pip.
+
+Everything else in `assets/art` — the card back, the table surface, the panels
+and the buttons — was authored for this project in
+[`scripts/build-art.mjs`](../../../scripts/build-art.mjs) and carries no third
+party licence.
+
+## Note for whoever ships this
+
+LGPL-3.0 is a copyleft licence. It is usable in a closed-source game as long as
+the licensed part stays separable and replaceable and its source is available —
+which is why the SVGs are in the repository rather than deleted after the build.
+If that is not acceptable for this product, the 36 faces are the only thing that
+has to be replaced; nothing in the code depends on their appearance, only on the
+file names, which follow `<rank>_of_<suit>.png` (see `Card.assetName`).