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/import_library.py

@@ -6,11 +6,9 @@ python -m app.import_library /games --import --owner admin
 import argparse
 import asyncio
 import json
-from pathlib import Path
-import tempfile
 import sys
+from pathlib import Path
 
-from app.converter.archive import ArchiveError, extract
 from app.converter.compatibility import CompatibilityError, Issue
 from app.converter.preflight import inspect_archive, inspect_directory
 
@@ -52,6 +50,7 @@ def check(source: Path) -> dict:
 
 async def import_one(source: Path, report: dict, username: str | None) -> dict:
     from sqlalchemy import select
+
     from app.db import SessionLocal
     from app.models import Game, GameVersion, Role, User
     from app.worker import convert