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/auth.py

@@ -1,9 +1,10 @@
-from fastapi import APIRouter, HTTPException, Response, status
+from fastapi import APIRouter, HTTPException, Request, Response, status
 from sqlalchemy import select
 
 from app.config import get_settings
 from app.deps import DB, SessionUser
 from app.models import User
+from app.ratelimit import client_ip, login_limiter
 from app.schemas import ChangeCredentialsIn, LoginIn, MeOut
 from app.security import (
     COOKIE_NAME,
@@ -30,10 +31,19 @@ def _set_cookie(response: Response, user: User) -> None:
 
 
 @router.post("/login", response_model=MeOut)
-async def login(body: LoginIn, response: Response, db: DB) -> User:
+async def login(body: LoginIn, request: Request, response: Response, db: DB) -> User:
+    keys = (f"ip:{client_ip(request)}", f"user:{body.username.lower()}")
+    if wait := login_limiter.retry_after(*keys):
+        raise HTTPException(
+            status.HTTP_429_TOO_MANY_REQUESTS,
+            f"Слишком много неудачных попыток входа. Повторите через {wait} с",
+            headers={"Retry-After": str(wait)},
+        )
     user = await db.scalar(select(User).where(User.username == body.username))
     if not user or not user.is_active or not verify_password(user.password_hash, body.password):
+        login_limiter.fail(*keys)
         raise HTTPException(status.HTTP_401_UNAUTHORIZED, "Неверный логин или пароль")
+    login_limiter.reset(*keys)
     _set_cookie(response, user)
     return user