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/tests/test_tomie_format.py

@@ -6,11 +6,11 @@ import pytest
 def test_native_translation_and_mod_edits_rebuild_the_same_vm_input(tmp_path, monkeypatch):
     from app import mods
     from app.config import get_settings
-    from app.converter.naninovel import _convert_package
     from app.converter.nani_package import Package, text_records
+    from app.converter.naninovel import _convert_package
     from app.converter.tomie_format import unpack_modules
     from app.converter.tomie_profile import PROFILE
-    from app.translation import apply_changes, text_index, locale_tables
+    from app.translation import apply_changes, locale_tables, text_index
     monkeypatch.setenv("DATA_DIR", str(tmp_path / "data"))
     get_settings.cache_clear()
     package = Package(profile=PROFILE, defaults={"points": 3}, function_data={"names": ["Tomie"]})