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/converter/tomie_validation.py

@@ -9,7 +9,6 @@ from app.converter.compatibility import Issue
 from app.converter.nani_expr import assignment, parse
 from app.converter.tomie_profile import FUNCTIONS, validate_expressions
 
-
 ARGUMENTS = {
     "ModifyBackground": "AppearanceAndTransition Duration Scale TintColor",
     "ModifyTextPrinter": "Duration HideOther IdAndAppearance MakeDefault ScenePosition",