chore: add CI, lint config, login rate limit and split large modules

- Rate-limit failed logins (8 per 15 min per IP or username, 429 + Retry-After)
- Add ruff/mypy config and GitHub Actions workflow (ruff, pytest, tsc, tests, build)
- Apply ruff autofixes (import order, pyupgrade)
- Extract rpy_helpers.py, engine-util.ts, TranslationParts.tsx and
  translation-types.ts from oversized modules
- Add dependency-free React UI tests
- Refresh README and ARCHITECTURE (Naninovel/Tomie, status and plans)

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

backend/app/routers/games.py

@@ -7,11 +7,11 @@ from sqlalchemy import and_, exists, func, or_, select, true
 from starlette.concurrency import run_in_threadpool
 
 from app.blobs import put_bytes
-from app.uploads import remove_upload
 from app.deps import DB, CurrentUser, has_perm, require
 from app.models import Game, GameVersion, User
 from app.schemas import GameDetailOut, GameIn, GameOut, GameUpdateIn, VersionOut
 from app.translation import version_languages
+from app.uploads import remove_upload
 
 router = APIRouter(prefix="/api/games", tags=["games"])
 Player = Annotated[User, Depends(require("games.play"))]