feat: add ATL animation timelines and try/raise to the Ren'Py player

Python sandbox
- try/except/else/finally, raise (incl. re-raise), assert, for/while ... else
- Multi-generator and dict comprehensions
- Builtin exception hierarchy; user exceptions subclass it
- Inside try, missing keys/indexes, division by zero, attribute access on None
  and unknown names raise Python exceptions; lookups stay lenient elsewhere
- int()/float() raise ValueError on non-numeric strings

ATL
- converter/atl.py: set/move (linear, ease, easein, easeout), pause, repeat,
  parallel, choice, block, on show/hide and named transforms become a timeline
  shipped as game.json "atl"; Move() becomes a linear slide
- player/atl.ts: timeline runner wired into the renderer; `on hide` plays
  before the picture is removed
- function, time, contains, matrixcolor and expressions still block the import

Tests: exceptions/ATL fixtures and runtime tests, converter ATL tests; README
and ARCHITECTURE updated.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -145,7 +145,8 @@ LOCKED`), Redis не нужен.
 
 Планы:
 
-* поддержка `screen`-языка и ATL-анимаций с движением в IR;
+* поддержка `screen`-языка и ATL `function`/`matrixcolor`/шейдеров (базовый ATL
+  с движением уже есть: `backend/app/converter/atl.py`, `frontend/src/player/atl.ts`);
 * другие движки (TyranoBuilder, RPG Maker MV) через тот же IR;
 * дальнейшее дробление `engine.ts` на модули (рендер сцены, UI, сохранения);
 * типизация backend под `mypy` (сейчас проверка справочная).